Redundancy systems. Classification of systems redundancy methods

Classification of backup methods

INCREASE RELIABILITY

RESERVATION AS A METHOD

Reservation- this is one of the main means of ensuring a given level of reliability (especially reliability) of an object with insufficiently reliable elements.

Redundancy is the use of additional means and (or) capabilities in order to preserve the operational state of an object in the event of a failure of one or more elements. That. Is a method of increasing the reliability of an object by introducing redundancies... In turn, redundancy is additional means and (or) capabilities that are extremely necessary for the object to perform the specified functions. The task of introducing redundancy is to ensure the normal functioning of an object after a failure occurs in its elements.

According to the type of reservation, the following classification of reservation methods is adopted(fig.10.1).

Structural(hardware, element, circuit) provides for the use of reserve elements of the object structure. The essence of structural redundancy is that the minimum required option additional elements are introduced.

Elements in the structural diagram are divided into the main(an element necessary for the object to perform the required functions in the absence of failures of its elements and reserve(an element designed to perform the functions of the main element in the event of a failure of the latter). The definition of the main element is not related to the concept of the minimality of the main structure of the object, since the element, which is the main one in some modes of operation, can serve as a reserve one in other conditions. Redundant element - the main element, in case of failure of which a reserve element is provided in the facility.

Time reservation associated with the use of reserve time. In this case, it is assumed that the time required for the object to perform the necessary work is obviously greater than the minimum required. Time reserves can be created by increasing the performance of the object, the inertia of its elements, etc. For chemical engineering facilities, this type of redundancy is implemented using the following techniques and operations:

1) an increase in operating conditions of the estimated operating time required to fulfill the set goal or to produce a given amount of chemical products;

2) devices and machines are developed for a greater value of productivity than is required by calculation, and, therefore, objects can complete the task in a shorter period of time than is established by the plan;

3) introduction into the structure of the technological scheme of intermediate containers (tanks and bins for accumulating the product) between the individual production devices. This technique creates conditions that allow the operation of the technological scheme to continue, even if part of the equipment before the intermediate tank or hopper is stopped. A similar function is also performed by gas tanks, warehouses, etc .;

4) the functional inertia of objects, for example, the thermal inertia of the furnaces, caused by the lining arrays, prevents a rapid decrease in the furnace temperature during an interruption in the fuel supply. The inertia of objects allows for the shortest possible period of time to eliminate the accident by switching the process to some reserve object or performing any other operations.

Information reservation Is a reservation using information redundancy. Examples of information reservation are multiple transmission of the same message over a communication channel; the use of various codes when transmitting information through communication channels that detect and correct errors that appear as a result of equipment failures and the influence of interference; the introduction of redundant information symbols in the processing, transmission and display of information. The excess of information allows you to compensate for distortions of the transmitted information or eliminate them.

Functional redundancy- redundancy, in which a given function can be performed in various ways and technical means.

For example, to manufacture a part, a group of machines is used, each of which can perform one of the sequential machining operations. In this case, the introduction of a universal or multi-operation machine into the production line will be functional redundancy. Another example is the creation of structurally combined reaction-mass transfer processes occurring in one apparatus of chemical technology. Functional redundancy also includes production redundancy (for example, the manufacture of products with a higher accuracy class), which is often used to ensure and improve the reliability of chemical engineering facilities. At the same time, conditions are created to increase reliability and durability, since first, in the process of operation, the object wears out to the traditional class of accuracy, and then the usual wear process takes place.

Load(or mode) redundancy - redundancy with the use of load reserves - provides for the use of the facility's ability to perceive additional, or redundant, loads. In chemical engineering, it is implemented by introducing safety factors, reducing the permissible operating parameters (pressure, rotational speed).

Redundancy in the chemical industry is widely used to improve the reliability of power supply systems (electricity, heat, water supply), devices that ensure the safety of the process are backed up (several safety valves are installed on one high-pressure tank).

Rice. 10.1 Classification of backup methods

Redundancy allows you to create objects, the reliability of which is higher than the reliability of their constituent elements, however, the possibilities of using redundancy are limited due to the increase in the mass and production area of ​​the system and because of the increase in the cost of a unit of product in comparison with the non-redundant one. This leads to the problem of choosing the optimal method of redundancy and the optimal number of spare elements.

For the analysis of the structural reliability of technical systems, of interest is structural redundancy- introduction into the structure of the object of additional elements that perform the functions of the main elements in the event of their failure.

Classification different ways structural redundancy is carried out according to the following criteria:

1) according to the scheme of switching on the reserve :

- general reservation, in which the object as a whole is reserved;

- separate redundancy in which individual elements or their groups;

- mixed reservation, in which different types of reservation are combined in one object;

2) by the method of switching on the reserve :

- permanent redundancy, without restructuring the object in the event of a failure of its element;

- dynamic redundancy, in which, when an element fails, the structure of the circuit is rebuilt. In turn, the dynamic subdivided into a:

a) redundancy by replacement, in which the functions of the main element are transferred to the backup only after the failure of the main one;

b) sliding redundancy, in which several main elements are backed up by one or more reserve elements, each of which can replace any main one (those groups of main and reserve elements are identical).

3) according to the mode of operation of the reserve :

Loaded redundancy, in which the redundant elements (or one of them) are in the primary element mode;

Lightweight redundancy, in which the backup elements (at least one of them) are in a less loaded mode compared to the main ones;

Unloaded redundancy, in which the backup elements are in the idle mode before they begin to perform their functions.

4) according to the conditions of restoration of working capacity during operation:

Redundancy with restoration;

Backup without recovery.

The main characteristic of structural redundancy is the redundancy ratio - the ratio of the number of reserve elements to the number of redundant (main) elements. Reservation can be with integer and fractional multiplicity (like 2: 3; 4: 2, etc.).

Redundancy of one main element with one reserve (i.e. with a multiplicity of 1: 1) is called duplication.

In case of redundancy with fractional multiplicity, the normal operation of the redundant connection is possible provided that the number of serviceable elements is not less than that required for normal operation. In case of redundancy with fractional multiplicity, one reserve element of the system falls on two or more main elements. Fractional redundancy also includes a rolling (floating) reserve.

In chemical engineering, the reliability of non-renewable redundant devices and technological lines, as a rule, is increased due to:

- general and separate redundancy with a permanently included reserve;

- general and separate redundancy by means of replacement;

- system redundancy with a sliding (floating) reserve.

The use of this type of structural redundancy as sliding is possible only if there is a special diagnostic device that allows you to find a faulty element and connect a backup one instead. In this case, the backup elements must be of the same type. However, this type of redundancy provides the greatest reliability gain.

Quantitatively, the increase in system reliability as a result of redundancy or the use of highly reliable elements can be estimated by the reliability gain, defined as the ratio of the reliability indicator before and after the system transformation

Structural diagram of the reserve group, consisting of one main and m backup elements is shown in Fig. 20.3.3.1.

Rice. 10.2. Block diagram of the system from one main and m backup elements

If a system is given with a permanently switched on reserve, consisting of two parallel operating elements (Fig.10.2, m= 1) with the probability of failure-free operation of the main element R 1, reserve - R 2, then the probability of failure-free operation of such a system is

P(t) = 1 – (1 – p 1 (t)) (1 – p 2 (t))

In the case of equally reliable elements:

P(t) = 1 – (1 – p 1 (t)) 2 = 2R 1 – R 1 2 = R 1 (2 – R 1). (10.1)

For an exponential distribution of failures of each of two parallel operating elements p 1 (t) = p 2 (t) = exp (–l t) taking into account (10.1), the probability of failure-free operation of the system is defined as P(t) = 2e- l t – e-2 l t.

Since the MTBF of one non-redundant element is:

the mean system uptime will be:

Then the reliability gains for the system. consisting of two parallel working elements, in comparison with one non-redundant element is equal to:

The probability of failure-free operation of a system consisting of one main and m redundant non-equidistant elements (Figure 10.2), is determined by the formula:

In the case of equally reliable elements, this formula will take the form:

For an exponential distribution of the probability of failure-free operation of elements, i.e. p(t) = e- l t, we get:

For small t there is a simple lower bound:

where i- failure rate i th element.

With identical elements, the previous formula takes the form:

Reliability gain W T(2) by the mean time of failure-free operation of the system, consisting of ( m+ 1) equally reliable elements operating in parallel, in comparison with the mean time of failure-free operation of one non-redundant element, provided that the probability distribution law of failure-free operation of each element is exponential, is equal to:

Mean time to system failure T(Fig.10.2) in the general case can be found only by numerical integration by the formula

For identical elements, mean time to failure with the probability of failure-free operation of the elements R(t) = exp (–l t) given is defined as:

For large values m :

10.2.1 According to the scheme of switching on the reserve at general reservation the object as a whole is reserved. At separate reservation individual elements (subsystems) of the object or their groups are reserved.

Examples of general redundancy (Fig. 10.3, a) are standby technological lines or units of large unit capacity. In case of separate reservation (Fig. 10.3, b), individual elements of the object are reserved.

Rice. 10.3. Redundancy schemes for a system consisting of n main elements: a) general redundancy with a permanently included reserve (the number of reserve circuits m= 1); b) separate (element-by-element) duplication with a permanently included reserve

For a system with serial connection n elements with general redundancy (duplication) (Figure 10.3, a), the probability of failure-free operation is equal to:

With separate redundancy (duplication) (Figure 10.3, b):

The system reliability gains in terms of the probability of no-failure operation for these two cases are, respectively, equal:

It follows that separate redundancy is more efficient than general redundancy: for example, for a system of three identical elements ( n= 3) for R = 0,9 R = 0,9 3 = 0,729; R (1) = 0,729(2 – 0,729) = 0,9266, R(2) = 0.729 (2 - 0.9) = 0.9703. Then: G p (1) = 1,27; G p (2) =1,33.

Separate redundancy, all other things being equal, gives a greater gain in reliability than general redundancy. Separate redundancy is especially beneficial when there is a large number of elements in the system and when the redundancy rate is increased.

The probability of failure of a system consisting of n elements (one main and ( n- 1) reserve), without taking into account the reliability of the switches, is calculated by the formula

Serial connection system n elements with shared redundancy ( m backup circuits) will function normally while maintaining the operability of at least one of them.

For a general redundancy scheme with a constantly switched on reserve, the probability of failure-free operation of the system (Figure 10.4), FBG is equal to (the elements are equally reliable, the probability of failure-free operation of each element is p(t)):

In turn, trouble-free operation i-th chain ( i = 1, ..., m) will take place during the trouble-free operation of each of n elements. Then:

Here: p ij- probability of failure-free operation j th element i-th chain ( j = 1, ..., n); n- the number of connected circuit elements in series.

Rice. 10.4. Block diagram of shared redundancy with always-on redundancy system with daisy-chain connection n elements

For the case when all elements are equally reliable (with the probability of failure-free operation equal to R), the probability of failure-free operation of the main system from n elements (random and independent failures) is equal to:.

Consequently, the probability of failure of the entire system consisting of one main and m backup systems will be equal to:

Then the probability of failure-free operation of the system with shared redundancy is equal to:

If the failure rate is constant, i.e. R(t) = exp(–L t), then using (10.5), we can find the reliability gain W T(3) by the mean time of failure-free operation during the operation of the system consisting of ( m+ 1) redundant systems operating in parallel (Figure 10.4) compared to the mean uptime of a non-redundant system:

Reliability gain W T(4) by the mean time of failure-free operation during the operation of the system, consisting of ( m+ 1) parallel operating backup systems (Fig.10.4), compared with the average uptime of one element:

Consider the case of a system with separate redundancy with a constantly included reserve, assuming that all elements are equally reliable with probabilities of failure-free operation p(t) (fig.10.5).

Rice. 10.5. Block Diagram of Split Redundancy with Always On Redundancy System with Daisy Chain n elements

For a system with separate redundancy, using formula (10.14), the probabilities of failure-free operation of individual redundant elements can be determined. Then the overall probability of no-failure operation of the split-redundant system is determined by the formula:

For the case when all elements are equally reliable, the probability of failure-free operation of the system with separate redundancy is equal to:

The gain in reliability in terms of the average uptime when the redundant system is operating in comparison with the average uptime of the main system with an exponential distribution law:

10.2.2 By the method of switching on the reserve. Redundant elements can be constantly switched on for the entire period of operation - to apply permanent redundancy (redundancy with a permanently switched on reserve without switching) or only in case of failure of the main ones - redundancy by replacement.

With constant redundancy, the backup elements are connected to the main ones during the entire operation time and are in the same operating mode with them. Continuous switching on of the reserve is the only possible one in systems where even a short interruption in operation is unacceptable (for example, in control systems of technological processes). Although it is simple (there are no switches and short stops in the operation of devices), the main disadvantage of permanent redundancy is the increased resource consumption of reserve elements. In this way, pumps, filters, etc. are usually backed up.

If it is not possible to apply the constant parallel operation of devices in chemical engineering, then it is necessary to use replacement reservation ("Substitution with unloaded reserve"). Substitution is performed automatically or manually.

In case of redundancy by replacement (or "replacement with an unloaded reserve"), the system is designed in such a way that when an element fails, it is rebuilt and restores its operability by replacing the failed element with a reserve one. In this case, adjustment is not required at the time of switching on the backup element; The backup device can be in a “warm” or “cold” state before it is put into operation - this preserves the reliability resource of each of the devices and increases the overall reliability of the entire system. In the case of the same type of elements, several reserve (or one) can be used to replace the main elements in case of failure.

Rolling redundancy is a replacement reservation in which a group of primary elements is backed up by one or more redundant elements, each of which can replace any of the failed elements of this group.

Sliding redundancy is used to reserve several identical or interchangeable system elements with one or more redundant ones, and the redundancy can be both loaded and unloaded. The system will fail if the number of failed primary elements exceeds the number of redundant ones. With a sliding (floating) reserve, any of the reserve elements can replace any main element of the system (for example, refrigerators, pumps). The sliding reserve gives the greatest gain in increasing reliability, but its significant drawback is that it is possible only for elements of the same type (subsystems).

The sliding redundancy scheme in the monoethanolamine purification unit is shown in Figure 10.6.

Rice. 10.6. Scheme of sliding redundancy in the monoethanolamine purification unit:

1 - absorber; 2, 3 - pumps; 4 - regeneration unit; 5 - standby pump

With a loaded sliding redundancy with ideal switches, the calculation of the system reliability is similar to that of the system of the type " m from n". If the failure rates of the main and backup elements are constant and the same, then the probability of failure-free operation of the system consisting of n major and m reserve elements in the loaded reserve mode can be determined by the formula:

If the probability of failure-free operation of the elements obeys an exponential law, then the mean time between failures of the system can also be calculated:

In the case of unloaded sliding redundancy, in the general case, the characteristics of the system reliability are expressed by complex formulas. However, if the failure rates of the main and backup elements are constant and the same, i.e., the probability of failure-free operation of the elements obeys an exponential law, then the probability of failure-free operation of a system consisting of n major and m reserve elements, in the unloaded reserve mode, can be determined by the Poisson formula:

Since with unloaded sliding redundancy, the total failure rate is n and the system will fail at the moment of failure ( m+ 1) th element, mean time between failures of the system:

10.2.3 According to the mode of operation of the reserve. The calculation of systems with loaded redundancy is carried out according to the formulas of sequential and parallel connection elements. In this case, it is considered that the failure of the backup group, consisting of the main and backup elements, will occur when its last element fails, and the backup elements operate in the main mode both before and after their failure, therefore the reliability of the backup elements does not depend on the moment of their failure. transition from the standby to the main state.

When backing up by substitution, three types of operating conditions for the backup elements are possible until they are put into operation:

a) loaded (hot) reserve ... The external conditions of the reserve completely coincide with the conditions in which the working apparatus is located. The reserve elements operate in the same mode as the main element, their reliability (the probability of failure-free operation) does not depend on the moment at which they were switched on in place of the main element. In this case, the resource of the reserve elements of the object begins to be consumed from the moment the entire system is turned on;

b) unloaded (cold) reserve ... The reserve elements are turned off and by condition (until they are turned on in place of the main one) they cannot fail. The external conditions in which the reserve is located are so much easier than the workers that practically the reserve elements begin to consume their resources only from the moment they are put into operation instead of the failed element.

v) light (warm) reserve ... The external conditions affecting the device before it is put into operation are lightweight. The reserve elements are in a light mode until they are switched on in place of the main one. While waiting in the reserve, they can fail, but with a probability less than the probability of failure of the main element (the reserve being in lighter conditions than the main element).

MTBF system with m-fold total loaded reserve can be found from the expression:

In the case of an exponential law of reliability of elements, we get:

where L = 1 / T O Is the failure rate of the circuit.

After integration, we represent (10.27) in the form of a finite difference:.

Substituting into this equation sequentially m= 1, 2, 3, ..., we get:

When redundancy is not loaded by substitution, the reserve elements are switched on when the main one fails, then the first reserve one, etc., therefore, the reliability of the elements at each moment of time depends on the moment of their transition from the standby state to the main one. In this case, it is considered that the replacement of a failed element with a reserve one occurs instantly, the system failure will occur when the last element fails. In an inoperative state, the element cannot fail and its reliability does not change.

Unloaded redundancy is common, since it is similar to replacing failed elements (parts, assemblies, assemblies) with spare ones.

There are four main ways to improve the reliability of complex systems and individual objects:

1) increasing the reliability of system elements. This is the usual, easy way, but to take advantage of it, you need more reliable components. But even if they are available, they are always much more expensive than the previous ones and an economic calculation is needed;

2) constructive measures to improve reliability (for example, damping possible vibrations, transition from a statically indeterminate structure to a statically determinate one, all kinds of protective coatings with hard metal, polymers, etc.). This path is associated with the technology of mechanical engineering and can also be the subject of a special study in the theory of reliability;

3) a radical change in the principle of functioning of the system for this purpose. Associated with creation new technology, this is a qualitative leap in the development of this industry - it arises from the economic inexpediency of previous engineering solutions.

4) the introduction of various types of redundancy.

Redundancy- these are additional tools and capabilities in excess of the minimum necessary for the object to perform the specified functions

The method of increasing the reliability of an object by introducing redundancy is reservation.

There are several methods increasing reliability due to redundancy. Distinguish redundancy:

Structural (redundancy in the structure - in the number of system elements);

Mode (redundancy in operating modes - in the number of system elements);

Temporary,

Functional,

Information

And a number of others.

Of greatest interest is structural, or circuit, redundancy, involving the use of redundant elements of the object structure.

1) By ways redundancy can be shared or separate (Figure 6.1).

Figure 6.1 - Classification of backup methods

1.1) General redundancy - the entire object, device or system as a whole is backed up (Figure 6.2):

Figure 6.2 - General redundancy

1.2) Separate redundancy - individual elements of the system are reserved (Figure 6.3). Separate redundancy is beneficial with a large number of devices and increasing the frequency.

Figure 6.3 - Split redundancy

Multiplicity of redundancy called the ratio of the number of reserve elements to the number of the main elements of the object.

2) Distinguish between redundancy with integer and fractional multiplicity:

2.1) integer redundancy is called a redundancy in which for normal operation of the connection it is enough that at least one device is in good order (i.e. one or more backup ones are assigned to the main pump);

Figure 6.4 - Reservation with integer multiplicity

2.2) fractional redundancy This is called a redundancy in which only one device can be faulty for the normal operation of the connection (that is, there is only one standby for several pumps).

Figure 6.5 - Fractional redundancy

Multiplicity number reservations:

where m is the total number of elements in the group;

r is the number of elements required for the normal operation of the system.

For example, let's analyze the circuits (Figure 6.6).

Figure 6.6 - Schemes with redundancy

According to the scheme in Figure 6.6, and we have a duplication and a multiplicity number

Integer multiplicity.

The diagram in Figure 8.6, b shows a diagram with a multiplicity

Integer multiplicity.

The diagram in Figure 8.6, c shows the "2 of 3" system

Fractional multiplicity.

3.1) When permanent reservation backup devices are connected to the main ones during the entire operation time and work simultaneously with them.

3.2) For reservation by replacement backup devices replace the main ones after their failure.

4) There are three type of structured reservation: loaded reserve, light reserve, unloaded reserve.

4.1) Loaded reserve- such a reserve, when the backup elements operate in the same load mode as the main element, i.e. the main element and the backup one lose reliability at the same rate.

4.1) Lightweight reserve- such a reserve, when the elements operate in a weaker load mode than the main element, i.e. redundant elements lose their reliability more slowly in comparison with the main element.

4.1) Unloaded reserve- when the backup element practically does not bear any load and its reliability does not drop at all. These are spare parts in stock.

Figure 6.7 examines the reliability with loaded, light and unloaded reserves for a system of 1 main element and 1 standby.

Figure 6.7 - Types of redundancy

Loaded reserve (Figure 6.7a). At 0< t < t 0 функционируют оба элемента и их надежность падает одинаково. После отказа при t >t 0 the first one no longer works, and the second one continues to work with the same reliability along the same curve.

Lightweight reserve (Figure 6.7b). At 0< t < t 0 функционируют оба, но основной (кривая 1) теряет надежность быстрее, чем второй (кривая 2) при пониженной нагрузке. При t >t 0 the 2nd element operates at full load, its reliability drops along curve 2.

Unloaded reserve (Figure 6.7c). At 0< t < t 0 работает только 1-й элемент (кривая 1), а при t >t 0 only the second (curve 2), but it starts not from t = 0, but from t = t 0.

Thus, the reliability of the light reserve is higher than the loaded one, and the unloaded one is higher than the light one.

Lecture 6

Topic: Structural redundancy and its types

Plan

1. Classification of structural redundancy, basic definitions.

2. The main schemes for calculating the reliability by the method of switching on reserve elements: constant, separate, replacement, sliding.

3. Types of reserve elements and modes of operation with loaded, light and unloaded reserves.

4. Settlement and logic diagram of structural redundancy of a complex system.

5. Organization of a reserve at the level of elements, devices and IS systems.

Keywords

Redundancy, redundancy, calculation scheme, digital device, permanent redundancy, separate redundancy, replacement redundancy, loaded reserve, unloaded reserve, modes of operation, sliding reserve, switching circuit, reliability, reliability.

Redundancy is a method of increasing the reliability of an object by introducing redundancy. The task of introducing redundancy is to ensure the normal functioning of the system after the occurrence of failures in its elements.

Reservation can be structural, informational, temporary, programmatic. Information reservation provides for the use of redundant information. Temporary reservation– use of excess time. Software redundancy - redundant programs.

Structural redundancy means that additional elements and devices are introduced into the minimum required version of the system, the elements of which are called basic, or instead of one system, it is envisaged to use several identical systems. At the same time, redundant redundant structural elements take over the performance of working functions in case of failure of the main elements.

The listed types of redundancy can be applied either to the system as a whole, or to its individual elements or their groups.

In practice, structural redundancy has become widespread (Fig. 1).

Rice. 1. Ways to reserve a COP

According to the scheme of switching on reserve elements, there are permanent, separate redundancy, redundancy with replacement and sliding redundancy.

Permanent redundancy - this is such a reservation, in which the reserve elements participate in the operation of the facility on an equal basis with the main ones (Fig. 2).

For permanent redundancy in the event of a failure of the main element, no special devices are required to activate the reserve element, since it is put into operation simultaneously with the main ones.

The main parameter of the reservation is its multiplicity(degree of redundancy). Under the number of redundancymthe ratio of the number of reserve objects to the number of reserved (main) objects is understood.

Separate redundancy the method of increasing reliability is called, in which separate parts of the object are reserved (Fig. 2.3).

Rice. 2. General redundancy and continuous switching on of the reserve with always included reserve.

Rice. 3. Separate redundancy with always-on reserve

Reservation by replacement - this is redundancy, in which the functions of the main element are transferred to the backup only after the failure of the main one (Fig. 4 a, b). When using redundancy by replacement, monitoring and switching devices are required to detect the fact of failure of the main element and switch it from the main to the backup.

Rice. 4. a) General redundancy with the inclusion of a reserve by replacement.

b) Separate redundancy with the inclusion of a reserve by replacement.

Rolling reservation - This is redundancy by replacement, in which a group of the main elements of an object is backed up by one or more redundant ones, each of which can replace any failed element in this group.

Sliding redundancy is always active, there is always a switching device that detects the presence of a fault and switches on the redundant element (Fig. 5).

Rice. 5. Rolling reservation scheme

Types of backup elements depending on the operating mode

Depending on the operating mode, a distinction is made between:

Loaded reserve - the backup element is in the same operating mode as the main one. At the same time, it is assumed that the reliability characteristics of the backup elements during the period of their stay as backup and during the period of use instead of the main ones after the failure of the latter, remain unchanged.

Lightweight reserve - the backup element is in a less loaded mode than the main one. It is assumed that the reliability characteristics of reserve elements during their stay as reserve elements are higher than during the period of their use instead of the main ones after the failure of the latter.

Unloaded reserve - the reserve element practically does not bear the load. Such a reserve element, being in reserve, should not fail, i.e. possesses ideal reliability during this period. During the period of using this element instead of the main one after the failure of the latter, the reliability becomes equal to the reliability of the main one.

Distinguish between redundancy with integer and fractional multiplicity. To distinguish them, the multiplicity of redundancy is indicated on the diagramm(Fig. 6, a, b).

Rice. 6. Redundancy: a) permanent redundancy with fractional multiplicity (m=4/2);

b) split redundancy with fractional multiplicity (m=2/4)

When reserving with integer multiples, the value m there is an integer, when reserved with a fractional multiplemis a fractional irreducible number. For example,mIfm= 4/2 = 2, this means that there is an integer redundancy, in which the number of spare elements is 2, and the total number is 3.

To back up objects with the same items, you can use a small number of spare items to replace any failed master items (rolling backups).

Majority and combined redundancy

A special case of fractional multiplicity redundancy is majority redundancy, which is often used in discrete-acting devices (Fig. 7). In case of majority reservation, instead of one element (channel), three identical elements are switched on, the outputs of which are fed to the majority body M(voting element). If all the elements of this reserve group are in good working order, then at the entrance M three identical signals are received and the same signal enters the external circuit from the output M.

Rice. 7. Majority reservation (majority choice)

If one of the three backup elements has failed, then the input M two identical signals (true) and one false signal are received. At the exit M there will be a signal that matches most of the signals at its input, i.e. majority body, carries out the operation of voting or election by majority. Thus, the condition for the failure-free operation of the group under the majority reservation is the failure-free operation of any two elements out of three and the majority body within a given time.

The combined reserve is shown in Fig. 8 shows a redundant group that combines the advantages of a loaded reserve (continuity of operation) and an unloaded reserve (providing a large gain in reliability). In this case, two elements form a duplicate group (loaded reserve), and the third is in an unloaded reserve. Such a reserve is called combined.

All types of structural redundancy can be used in critical IC devices (Fig. 9).

Rice. 8. Combined reserve

Rice. 9. Settlement and logic diagram of structural redundancy of a complex TS subsystem

Theoretically, by introducing redundancy into the structure of the system and choosing the optimal modes, it is possible to create an arbitrarily reliable CS. But this is not always practically feasible. Analyzing all types of redundancy, a practical conclusion should be drawn: it is not possible to ensure high reliability of the compressor station by means of a common loaded reserve for economic reasons. The greatest effect is given by element-by-element reservation [ 1, 2, 3, 6].

Comparing the types of redundancy with a loaded and unloaded reserve, one can notice that, all other things being equal, a system with an unloaded reserve is more reliable than a system with a loaded reserve.

Organization of a reserve at the computer and CS level

Computer-level redundancy. In general-purpose computer hardware, redundancy occurs at various levels. At the computer level, redundancy consists of the availability of a large number machines of the same type, which is necessary to solve the assigned tasks. In this case, the reliability of the system is assessed as for systems with sliding redundancy. In the case of general purpose computers, it is advisable to use the performance of all available processors. Then it is more convenient to characterize the property of the system through the effective performance of the system.

where P i- productivity (the number of tasks performed by the machine per unit of time)i th car;

n- the number of machines in the system;

TO i - availability factori th car.

If individual computer systems are connected through adapters between channels for peripheral devices, through a common memory field or in another way, form a multi-machine (multiprocessor) CS, then the effective performance of such a system

,

where m - the number of states of the system;

P j - the probability that the system is j -th state;

NS j- system performance in j -th state.

Probability P jdetermined by the method of Markov chains. Since the configuration of such systems can be very different, methods for calculating the reliability of systems with a complex structure, for example, the method of minimum paths and sections, should be used to assess the probability of maintaining the connectivity of the system.

Device-level redundancy ... At the lower levels of the structure hierarchy in universal computers redundancy occurs at the level of peripheral devices (PU). To solve problems, a certain minimum number of PUs is required.

Code-level redundancy - computers use error detection and correction codes to improve the reliability of RAM and ROM. The use of these codes makes it possible to correct a certain number of errors in transmission channels or restore information in the event of failure of some cells in RAM and ROM or tracks (i.e., read-write amplifiers) in magnetic disk drives. The reliability of such devices is assessed as the reliability of redundant sliding-reserve systems.

Redundancy in specialized and control computers ... In specialized, and especially in control machines, redundancy is used much more widely due to the high requirements for the reliability of such systems.

At the computer level, and sometimes at the software level, tripleting is used. There are also systems where multiple backup machines are used. In order to improve reliability, some of them can operate in the loaded reserve mode, some in the unloaded mode. However, computer-level backups are not the most economical. To increase reliability while limiting the mass, cost and overall dimensions of the compressor station, redundancy of individual machine devices is used by tripping or using several loaded or unloaded reserves. To increase the reliability of the most critical nodes, tripleting or interlacing logic is used (represented as a redundant logic circuit, where errors in one layer are corrected in the same or the next layer of logic elements).

All the considered methods of redundancy in the CS refer to passive redundancy, since they do not provide for system reconfiguration. Redundancy methods providing for automatic reconfiguration of the system are used in fault-tolerant computer systems (OCS). The OCS uses the means of detecting, localizing the failure and means of reconfiguration.

Failures in the ACS are detected using control tools, and localized using diagnostic tools and eliminated by automatic reconfiguration of the system. Reconfiguration consists in rebuilding the structure of computing facilities in such a way that its failed parts are eliminated from participating in the work.

Control questions and tasks

1. What is a reservation?

2. What types of structural redundancy are widely used in practice?

3. What is persistent (shared) backups?

4. What is the value of the redundancy rate when duplicating?

5. Give an example of a combined reserve of CT elements?

6. Make a structural diagram of the reliability of a device consisting of four main elements included according to a separate redundancy scheme with a loaded reserve (m = 1).

7. How is UBR assessed in case of majority reservation?

8. Where is dynamic reservation used most often?

9. Make up the structural reliability of the CS device consisting of 4 main elements included according to the general redundancy scheme with a loaded reserve atm = 2.

10. Under what method of redundancy of IC devices are switching devices (switch) always present?

Literature: 1,2,3,5,6, 7.

Many people know various systems creating disk images and Reserve copy data such as Acronis True Image, Pagaron Drive Backup, Ghost, Time Machine for Mac-compatible computers, etc. Microsoft has also implemented a data backup system in its operating systems, which is available for both regular users and system administrators... Before the release of the operating system Windows Vista Microsoft offered users NTBackup and System Restore, which had a lot of flaws. With the release of Windows Vista and the transition to the VHD image storage format, it became possible to more easily backup data and create images of the operating system using a new set of utilities for Windows name Backup and Restore. After the release of new operating systems, this component has been improved and modified. In this article, we will look at what Microsoft offers to the end user for backing up data in the recently released Windows 8. But first, let's briefly talk about the main types of backups that are implemented in numerous products from various companies.

Types of backup

Backup is divided into various types depending on the tasks that are set before the person implementing it. software... In some cases, users only need to create copies of important files stored on disk; in others, they need to create full-fledged images of the operating system with the ability to roll back all previous changes. At the same time, system administrators are provided with the ability to centrally store data backups, which makes it easier to control backup versions and restore systems as needed. Naturally, depending on the selected type of backup, one or another algorithm for comparing and saving files is used - either byte-by-byte or sector-by-sector copying from the data source, when the information is exactly recorded on the backup medium. To restore files and data, you can also use the functions of file systems that support journaling and logging of changes - first a full snapshot of the file system is made, and the data is backed up as needed if individual files are marked as changed. File systems with enhanced version control are best suited for this case, as they significantly save space on the backup media. In addition to the traditional creation of backup copies of files that are not currently in use, there are real-time backup algorithms. In this case, the backup occurs even when the file is open in any program. This opportunity is achieved through the use of snapshots of file systems and is actively used, for example, in virtualization systems for working with virtual disk drives. The data backup process can take place in several ways. Let's consider the most common ones.

Cloning partitions and creating images

Cloning means copying a partition or partitions of a disk with all files and directories, and file systems to a backup medium, that is, creating a complete copy of data on another medium. It requires a large number space on the backup media, but at the same time allows you to achieve the most complete backup of an individual PC or data disk. Also, special mention should be made of cloning the system in the form of a special image - a virtual drive, that is a separate file, which can contain several disk partitions. Such an image can be created by means of the operating system itself. It allows you to reduce the amount of data, and also provides the ability to subsequently work with it as with a regular disk, or connect it to virtual machines, which simplifies the transfer of operating systems from one server or computer to another. Today, virtual images are gaining popularity due to the flexibility of connection, as well as cross-platform and easy transfer from one computer to another. As a rule, cloning or creating an image for backup is quite rare, since the space occupied backup copy, very big. Similar procedures are used in most cases to create a copy of the operating system with all files, and not to back up individual data on disk. For backing up user data that is frequently changed or used in work, another type of backup is widely used - full file backup.

Full file backup

This type of backup involves creating duplicates of all files on the media. simple method- copying from one place to another. Full file backups, due to the length of the process, are usually carried out outside business hours due to too large amounts of data. This type of reservation allows you to save important information, but due to the long backup times, it is not very suitable for recovering rapidly changing data. It is recommended to carry out full file copying at least once a week, and it is even better to alternate it with other types of file copying: differential and incremental.

Differential redundancy

Differential backups only copy files that have changed since the last full backup. This allows you to reduce the amount of data on the backup media and, if necessary, speed up the data recovery process. Since differential backups are usually performed much more frequently than full backups, it is very effective because it allows you to recover the most recently changed data and track the history of file changes since the full backup.

Incremental backup

Incremental backups are slightly different from differential backups. It implies that on first launch, only those files are backed up that have changed since the last time a full or differential backup was in progress. Subsequent incremental backups only add files that have changed since the previous backup. In this case, the changed or new files do not replace the old ones, but are added to the medium independently. Of course, in this case, the history of file changes increases with each stage of the backup, and the process of restoring data for this type of backup takes much longer, since it is necessary to restore the entire history of file changes, step by step. However, with a differential backup, the restore process is simpler: the master copy is restored and the latest differential backup data is added to it.

Many backup software packages use different types of backups, and often combine them for greater efficiency and space savings. Systemic Windows utilities, which we will discuss in this article, also use various types of backups, which allows you to more dynamically and quickly restore user data, depending on the situation. For server operating rooms Windows systems There are more recovery utilities available than for Windows desktop operating systems, but here we will consider only those that are available to ordinary users. Moreover, for different editions of Windows, the set of components differs, which is due to the division of operating systems into corporate and home. For Windows operating systems, there are two main utilities for backing up data, which differ in the type of backup.

Windows Backup And Restore

The Windows Backup And Restore component became available to users since the release of the Windows Vista operating system and is responsible for creating a full backup of the operating system with the option of incremental backups. With the release of the Windows 8 operating system, this component changed its name to Windows 7 File Recovery. Although it has not lost anything of its functionality, Microsoft recommends using the new File History utility for backing up data, which is included in Windows 8 and Server 2012 operating systems, but we will talk about it a little later. Windows Backup And Restore allows you to create an automatic full backup to removable media, optical discs or to a special location on a remote server.

The latter feature is available only for certain editions of Windows 7/8, as it is positioned as a solution for IT administrators of companies. A full system backup in the case of using this component assumes not only saving user files, but also the ability to create an image of the entire operating system and backup individual computer disks. The user is also available to create an exclusively system image, which can later not only be removed to a new media of this computer, but also used as virtual disk in virtualization systems. If this component is used, the user can specify the folders that need to be backed up, as well as specify those system disks that need to be saved with a full backup. When backing up only user files, Windows Backup And Restore uses incremental data backups, which allows you to get more snapshots of files at different points in time. Typically, a full backup is performed once a week and involves not only backing up user files, but also creating a system image and copying data for Windows System Recovery component restore points. The process of restoring user files can take place directly from the operating system - it is quite simple and straightforward for most users. System recovery in case of a serious failure can be carried out using the built-in utilities Windows Recovery... To do this, you must either create a new special recovery disc, or use the installation image of the operating system from which it was previously installed on the PC. When loaded in mode Windows recovery Recovery will offer the user a choice of the following recovery modes: file recovery, go to a specific recovery point, extract a system backup image to the main system drive. In this case, data for recovery can be taken from optical media, external or internal storage, as well as from network storage. The edition of the operating system does not play a role in this case. Alas, despite the fact that Windows Backup And Restore is a fairly powerful and convenient component of the operating system, Microsoft said that, according to research, 5% of users use this utility at best. In this regard, for easier and more efficient data backup, Microsoft has developed for users the next generation of system backup - Windows File History.

Windows File History

Windows File History, a new component of Windows 8 and Server 2012 operating systems, in some way replaces its predecessor - Windows Backup And Restore. It is intended to replace only incremental file backups, while system imaging and full backups can only be performed with using Windows 7 File Recovery. Windows File History was designed from the ground up to be a convenient and practical solution for users who need a transparent way to back up their important data. When developing this utility, special attention was paid to the ease of initialization of the process, combined with the possibility of a convenient and quick view all saved data. The process of backing up with the help of the new utility goes unnoticed for the user in automatic mode and does not require additional actions from him. It should be noted that the reservation has been modified by network devices, which makes it easy and convenient to work with saved files if used mobile connections or weak communication channels.

The Windows File History utility was based on a part of the basic functionality of Windows Backup And Restore, in which the visual component responsible for the presentation of saved user data was reworked. Previously saved data can now be viewed from file manager Windows Explorer using a separate History tab. This allows you to quickly find required files and restore them to any location in the system. Despite the fact that the backup process is based on an incremental backup, when working with it, there is no thought that this is a backup, it is rather a history of creating, modifying or deleting user files, available at any time. This approach to data backup, of course, will suit most inexperienced users, since the process is convenient and more intuitive to use than working with Windows Backup And Restore.

To back up data using Windows File History, you can use optical media, external drives, or network attached storage. Of course, storing data on optical media is more a tribute to tradition than a real method of using incremental backups, because data can change very often. The best choice for ordinary users, backing up to an external or internal drive is the option.

For ease of use in Windows 8, each pluggable external drive can be used as a backup tool using Windows File History. So, if the drive is connected, there is now a separate tab in the options of the drop-down menu at autostart, which allows you to designate the connected drive as a drive for backup in one click. In this case, even if the disk was subsequently disconnected from the system, data backup will resume as soon as it is installed back. A similar approach is used in the case of data backup to network storage. Disconnect from local network will not affect the operation of the system in any way, and when a network environment appears operating system will automatically start a new backup cycle according to the schedule. Transparent activation system Windows functions File History is a really huge plus for the user.

By default, backups through the Windows File History utility occur every hour, however, if necessary, the user can choose the time intervals between each data backup. The user has the ability to set intervals between reservations from 10 minutes to 1 day. For Windows File History, only one current backup location can be set, however, if you add multiple drives to the backup locations, they can be used alternately depending on their availability. This is convenient when using network storage and a separate drive. This way, the data will be saved in multiple locations depending on the current configuration. Also, one cannot fail to note the function of selecting the number of depths of saved copies. For example, after one or several months, the system can automatically overwrite old data, replacing it with new ones. This saves space where data is backed up. In addition, the user can use up to 25% of the storage space for data backups.

The Windows File History utility backs up the most frequently used folders by default, namely Contacts, Favorites, and Desktop. In addition, the reservation is automatically applied to all used Libraries folders. The user can create their own data libraries, which are, in fact, symbolic links to real computer folders. That is, if the user needs to reserve a specific folder on the PC, before installing Windows File History you need to add this folder to libraries. In addition, if some folders need to be excluded from the reservation, then the user can selectively exclude all of the user's libraries or a set of frequently used folders. Taking into account the active integration with the function of "cloud" data storage Windows Skydrive the use of this "cloud" service can be aimed at backing up important user data stored in the "cloud". In order for such a bundle to work, you just need to install Skydrive - after that it will automatically be added to the libraries and will be backed up as needed. Alas, the function of backing up data to the "cloud" is not yet available to users, but Microsoft is already planning to add a certain option for backing up data to "cloud" data storage in future versions of its OS.

Thus, new system Windows File History backup is great for most users. A simple and intuitive interface with the ability to quickly add and restore files is much closer to a modern user than previous version incremental backups in Windows Backup And Restore.

In this article, we will acquaint the reader with the meaning of redundancy in the broad sense of this term. It will also consider its types, general presentation, relationship with natural phenomena and much more.

Introduction

Redundancy is a universal principle that ensures the reliability of any type of system. Such types of systems are widely distributed and used in nature, technology and engineering.

The types of redundancy include:

• hardware form of redundancy, a striking example of which is duplication;
• information type of redundancy, for example, a technique that detects errors and correlates them;
• temporary redundancy, which can be observed in the methodology of an alternative type of logic;
• reservation program type represented by functionally equivalent programs.

Technical systems

By definition, redundancy should be considered as a method that increases the performance and reliability of a particular device or mechanism. And also with the help of this phenomenon, you can maintain the device at a certain, necessary level by including a spare set of elements and communication. However, this is an additional maintenance measure imposed additionally.

This concept can be considered both in a narrow sense, for example, ticket reservation, and in a broad one, for example, the use of backup mechanisms at industrial facilities. However, in both cases, this will be a way to prevent possible malfunctions in the future development of events, which would lead to a violation of the integrity of the system in the long term. The main reason for the need for backup methods to maintain the system in a state of norm is dictated by a set of requirements for state industrial safety... Reservation is also of great importance in equipment intended for military craft.

With the help of this phenomenon, the safety of nuclear power plants is ensured, which are placed on a level with physical separations and a variety of types of equipment designed to implement the most important principles of a single form of failure.

Safety systems for such important facilities as nuclear power plants have a threefold redundancy option. The latest Russian projects implemented during construction in the PRC have a fourfold reservation.

The element of the device related to the minimized structures, which ensures its ability to perform work, is called the main one. Redundant elements are parts whose purpose is to ensure the operability of the mechanism due to the failure of the main parts.

In a technological system, redundancy can be classified according to a set of characteristics, the main among which are the height of the redundancy level, the multiplicity, the state of spare elements before they are put into operation, the ability of the main and spare parts to work together.

Failure of a part of the system in a product intended for backup can occur only after the main device and all spare elements of the system are out of operation. A group of elements can be called redundant, in which the failure of one of them or even more will not lead to a breakdown of the entire system. All parts of the mechanism capable of performing their functions will continue to do them, and the work of the missing spare parts is taken over by the backup device. This replacement method is called functional redundancy.

In accordance with the scale and unit of calculation, the following types of reservation are distinguished:

• general, in which a reserve is necessary to continue work only in cases of failure of the entire facility;
• separate, in which the reservation of separate parts of the object takes place;
• private, providing for the reservation of a group of the same set of elements.

Analyzing the backup systems, the person came to the conclusion that the level of failure rate of the redundant object increases with increasing time. A non-redundant structure has the same effect of time on the probability of failure in accordance with the redundant one. However, this does not indicate that the absence of a breakdown in the system and, therefore, not using the stock can justify its absence until the moment of the system failure. Based on the understanding of this phenomenon, we can conclude that redundancy makes sense to apply in systems required for short-term operation, and the critical system must be secured using other reliable methods.

It is important to consider the specifics of the purpose of the backup system. This is due to the fact that the method used to digital system with a continuous type of activity, will be of little use for a system with an analog type device. Due to all this, the problem arises with the creation of a backup method for all systems at once.

There is a method for assessing the effectiveness of redundancy, in which using the coefficient responsible for increasing reliability, the reliability indicators of the ratios are calculated:

yp = P (t) p / P (t)

γQ = Q (t) / Q (t) p

In such calculations, P (t) and Q (t) - indicate the possibility of failure-free operation and the chance of failure for the reserve system.

P (t) and Q (t) are the height of the probability of failure-free operation and the probability at which a failure of a non-redundant type of system will occur.

General type

In a general reservation, the stock is made at once for the entire system. Depending on the way in which the backup device was introduced, total redundancy can be considered on an ongoing basis and in replacement. In the case of using a general type of reserve, spare devices are connected to the main ones and remain included in them throughout the entire operating mode.

Constant type redundancy

A standing reservation is a form of stock in which there is relatively simple circuit construction, there are no interruptions in work even in cases of failure of some element.

The obvious disadvantage of a loaded reserve is an increase in energy consumption and "aging" of spare elements along with the main ones. As a result, the need to replace the elements of the main composition will determine the availability of replacement and spare.

Substitution

When reserving funds, any objects that can be used in order to resume the operation of the system in case of a failure, this process can occur by substitution.

Reservation by means of substitution can be performed by another automatic type system or by a human hand. In the case of using automatic intervention, it is necessary that the machine performing the work be highly reliable. Using manual element replacement increases the time spent switching. However, the high reliability of the operator replacing the part can be taken into account when comparing the work of a person and a machine.

Split in reservations

The separate type of redundancy provides for the introduction of an individual reserve intended for all parts of the non-redundant type of system. It is divided into general and substitute. Separate substitution is characterized by the probability of a failure in the system only if the failure occurs in one place twice. Mathematical analyzes show us that using split redundancy will give a higher rate of system reliability.

Relationship with biology

In biology, reservations can be traced by observing animals. For example, an organism located at the beginning of the food chain uses redundancy to ensure the reproduction of the species in the plural with the help of high fertility. The herbivore, in the predominant number of cases, has more offspring than the predator.

Reservation is a precautionary measure that is widely used by our body as well. An example is the duplication of external organs (two eyes, hands, ears and nostrils). Remembering the internal organs, duplicated sex glands and kidneys can be noted. The presence of this phenomenon in the body can increase its functional set of capabilities. Duplicated human eyes make it possible to realize vision in stereoscopic form.

The science that studies redundancy in living systems is called bionics.

Reservation and organizational systems

In an organizational system, reservation is the presence of an entity capable of performing the duties of the head of an entire object, project or enterprise, at the time of the absence of the head. For this, deputies are appointed to responsible positions. In most cases, there are several deputies responsible for different managerial functions.

Organizational systems like the army use the concept of a reserve, which is, in fact, a reserve of personnel.

Conclusion

Reserve can be called a synonym for the word "reservation". This phenomenon is widely used by all types of living and mechanized systems and underlies many of the most important biological phenomena and processes. There are many ways to perform the action in question, each of which has its own specifics and meaning. Redundancy has an unusually huge size diagram of the spectrum of parts of all living things to which it can spread.