RAID array. What is this? For what? And how to create?

Over many decades of development computer industry Information storage means for computers have gone through a serious evolutionary path of development. Punched tapes and punched cards, magnetic tapes and drums, magnetic, optical and magneto-optical disks, semiconductor drives - this is just a short list of already tested technologies. Currently, laboratories around the world are attempting to create holographic and quantum storage devices that will greatly increase the recording density and reliability of its storage.

In the meantime, the most common means of storing information on a personal computer has remained for a long time hard disks. Otherwise, they can be called HDDs (hard magnetic disk drives), hard drives, hard disks, but the essence does not change from changing the name - these are drives with a package of magnetic disks in a single housing.

First HDD, called IBM 350, was assembled on January 10, 1955 in the laboratory of the American company IBM. With the size of a good cabinet and a weight of a ton, this hard drive could hold five megabytes of information. From a modern point of view, such a volume cannot even be called funny, but during the mass use of punched cards and magnetic tapes with serial access, this was a colossal technological breakthrough.

Uploading the first hard drive IBM 350 from an airplane

Less than six decades have passed since that day, but now you won’t surprise anyone with a hard drive weighing less than two hundred grams, ten centimeters long and a volume of information of a couple of terabytes. At the same time, the technology for recording, storing and reading data is no different from that used in the IBM 350 - the same magnetic plates and read/write heads sliding above them.

The evolution of hard drives against the background of an inch ruler (photo from " Wikipedia " )

Unfortunately, it is precisely the features of this technology that cause two main problems associated with using hard disks. The first of them is the too low speed of writing, reading and transferring information from the disk to the processor. In a modern computer, it is the hard drive that is slow device, often determining the performance of the entire system as a whole.

The second problem is the insufficient security of information stored on the hard drive. If your hard drive breaks, you can irretrievably lose all the data stored on it. And it’s good if the losses are limited to the loss of a family photo album (although there is actually little good in this). The destruction of important financial and marketing information can cause the collapse of a business.

Partially helping to protect stored information is regular backup(backup) all or only important data on the hard drive. But even in this case, if it breaks down, that part of the data that has been updated since the last backup will be lost.

Fortunately, there are methods that help eliminate the above disadvantages of traditional hard drives. One such method is to create RAID arrays of several hard drives.

What is RAID

On the Internet and even modern computer literature You can often come across the term “RAID array”, which is actually a tautology, since the abbreviation RAID (redundant array of independent disks) already stands for “redundant array of independent disks”.

The title says it all physical meaning such arrays are a set of two or more hard drives. Collaboration These disks are controlled by a special controller. As a result of the controller's operation, such arrays are perceived operating system as one hard drive and the user may not think about the nuances of managing the operation of each hard drive separately.

There are several main types of RAID, each of which has a different impact on the overall reliability and speed of the array compared to single disks. They are designated by a conventional number from 0 to 6. A similar designation with detailed description architecture and operating principle of the arrays was proposed by specialists from the University of California at Berkeley. In addition to the main seven types of RAID, various combinations of them are also possible. Let's consider them further.

This simplest type an array of hard drives, the main purpose of which is to increase the performance of the computer's disk subsystem. This is achieved by dividing the streams of written (read) information into several substreams, which are simultaneously written (read) to several hard drives. As a result, the total speed of information exchange, for example, for two-disk arrays increases by 30-50% compared to one hard drive of the same type.

The total volume of RAID 0 is equal to the sum of the volumes of the hard drives included in it. Information is divided into data blocks of a fixed length, regardless of the length of the recorded files.

The main advantage of RAID 0 is a significant increase in the speed of information exchange between disk system without losing the useful capacity of hard drives. The disadvantage is a decrease in the overall reliability of the storage system. If any of the RAID disks 0 all information recorded in the array is irretrievably lost.

Similar to the one discussed above, this type of array is also the simplest to organize. It is built on the basis of two hard drives, each of which is an exact (mirror) reflection of the other. Information is written in parallel to both disks in the array. Data is read simultaneously from both disks in sequential blocks (parallelization of requests), due to which a slight increase in reading speed is achieved compared to a single hard drive.

The total capacity of RAID 1 is equal to the capacity of the smaller hard drive in the array.

Advantages of RAID 1: high reliability of information storage (data is undamaged as long as at least one of the disks included in the array is intact) and some increase in read speed. Disadvantage - buying two hard drives, you get the usable volume of only one. Despite the loss of half the useful volume, "mirror" arrays are quite popular due to their high reliability and relatively low cost - a pair of disks is still cheaper than four or eight.

When constructing these arrays, an information recovery algorithm is used using Hamming codes (an American engineer who developed this algorithm in 1950 to correct errors in the operation of electromechanical computers). To ensure the operation of this RAID controller, two groups of disks are created - one for storing data, the second group for storing error correction codes.

This type of RAID has become less widespread in home systems due to the excessive redundancy of the number of hard drives - for example, in an array of seven hard drives, only four will be allocated for data. As the number of disks increases, redundancy decreases, which is reflected in the table below.

The main advantage of RAID 2 is the ability to correct errors on the fly without reducing the speed of data exchange between the disk array and the central processor.

RAID 3 and RAID 4

These two types of disk arrays are very similar in design. Both use multiple hard drives to store information, one of which is used exclusively for storing checksums. Three hard drives are enough to create RAID 3 and RAID 4. Unlike RAID 2, data recovery on the fly is not possible - information is restored after replacing a failed hard drive over a period of time.

The difference between RAID 3 and RAID 4 is the level of data partitioning. In RAID 3, information is broken down into individual bytes, which leads to serious slowdown when writing/reading a large number of small files. RAID 4 splits data into separate blocks, the size of which does not exceed the size of one sector on the disk. As a result, processing speed increases small files, which is critical for personal computers. For this reason, RAID 4 has become more widespread.

A significant disadvantage of the arrays under consideration is increased load to a hard drive designed to store checksums, which significantly reduces its resource.

Disk arrays of this type are actually a development of the RAID 3/RAID 4 scheme. Distinctive feature is that a separate disk is not used to store checksums - they are evenly distributed across all hard drives array. The result of the distribution is the possibility of parallel recording on several disks at once, which slightly increases the speed of data exchange compared to RAID 3 or RAID 4. However, this increase is not so significant, since additional system resources are spent on calculating checksums using the “exclusive or” operation. At the same time, the reading speed increases significantly, since simple parallelization of the process is possible.

The minimum number of hard drives to build RAID 5 is three.

Arrays built using the RAID 5 scheme have very significant drawback. If any disk fails, after replacing it, it takes several hours to full recovery information. At this time, the intact hard drives of the array operate in super-intensive mode, which significantly increases the likelihood of failure of the second drive and complete loss of information. Although rare, this happens. In addition, during RAID 5 restoration, the array is almost completely occupied by this process and ongoing write/read operations are performed with large delays. If for the majority ordinary users This is not critical, but in the corporate sector such delays can lead to certain financial losses.

To a large extent, the above problem is solved by constructing arrays according to the RAID 6 scheme. In these structures, checksums are stored, which are also distributed cyclically and evenly across different disks, the amount of memory equal to the capacity of two hard drives is allocated. Instead of one, two checksums are calculated, which guarantees data integrity in the event of simultaneous failure of two hard drives in the array.

Advantages of RAID 6 - high degree information security and a smaller drop in performance than in RAID 5 during data recovery when replacing a damaged disk.

The disadvantage of RAID 6 is that the overall data exchange speed is reduced by approximately 10% due to an increase in the volume of necessary checksum calculations, as well as due to an increase in the volume of information written/read.

Combined RAID types

In addition to the main types discussed above, various combinations of them are widely used, which compensate for certain disadvantages of simple RAID. In particular, the use of RAID 10 and RAID 0+1 schemes is widespread. In the first case, a pair of mirrored arrays are combined into RAID 0, in the second, on the contrary, two RAID 0 are combined into a mirror. In both cases, the increased performance of RAID 0 is added to the information security of RAID 1.

Often in order to increase the level of protection important information RAID 51 or RAID 61 construction schemes are used - mirroring of already highly protected arrays ensures exceptional data safety in the event of any failures. However, it is impractical to implement such arrays at home due to excessive redundancy.

Building a disk array - from theory to practice

A specialized RAID controller is responsible for building and managing the operation of any RAID. Much to the relief of the average user personal computer, in most modern motherboards these controllers are already implemented at the chipset southbridge level. So, to build an array of hard drives, all you need to do is purchase the required number of them and determine the desired RAID type in the appropriate section BIOS settings. After this, instead of several hard drives in the system, you will see only one, which, if desired, can be divided into sections and logical drives. Please note that those who are still using Windows XP will need to install an additional driver.

External RAID controller with four SATA ports

Note that integrated controllers, as a rule, are capable of creating RAID 0, RAID 1, and combinations thereof. Creating more complex arrays will still require purchasing a separate controller.

And finally, one more piece of advice - to create a RAID, purchase hard drives of the same capacity, the same manufacturer, the same model, and preferably from the same batch. Then they will be equipped with the same logic sets and the operation of the array of these hard drives will be the most stable.

RAID arrays were developed to improve data storage reliability, increase processing speed, and provide the ability to combine multiple disks into one large one. Different types RAID decide different tasks, here we will look at several of the most common configurations of RAID arrays of the same size.

RAID 0

RAID 0(Stripe). The mode used to achieve maximum performance. The data is evenly distributed across the array disks and combined into one, which can be divided into several. Distributed read and write operations can significantly increase operating speed, since several simultaneously read/write their portion of data. The entire volume is available to the user, but this reduces the reliability of data storage, since if one of the disks fails, the array is usually destroyed and it is almost impossible to restore the data. Scope of application - applications that require high speeds of exchange with the disk, for example video capture, video editing. Recommended for use with highly reliable drives.

RAID 1

RAID 1(Mirror). Several disks (usually 2), working synchronously for recording, that is, completely duplicating each other. The performance improvement occurs only when reading. The most reliable way to protect information from failure of one of the disks. Due to its high cost, it is usually used when storing very important data. The high cost is due to the fact that only half of the total capacity is available to the user.

RAID 10

RAID 10, also sometimes called RAID 1+0- a combination of the first two options. (RAID0 array from RAID1 arrays). It has all the speed advantages of RAID0 and the reliability advantage of RAID1, while maintaining the disadvantage of the high cost of the disk array, since the effective capacity of the array is equal to half the capacity of the disks used in it. To create such an array, a minimum of 4 disks is required. (In this case, their number must be even).

RAID 0+1- RAID1 array from RAID0 arrays. In fact, it is not used due to the lack of advantages compared to RAID10 and lower fault tolerance.

RAID 1E

RAID 1E- An option similar to RAID10 for distributing data across disks, allowing the use of an odd number (minimum number - 3)

RAID 2, 3, 4 - various options distributed data storage with disks allocated for parity codes and various sizes block. Currently, they are practically not used due to low performance and the need to allocate a lot of disk capacity for storing ECC and/or parity codes.


RAID 5

RAID 5- an array that also uses distributed data storage similar to RAID 0 (and combining into one large logical one) + distributed storage of parity codes for data recovery in case of failures. Compared to previous configurations, the Stripe block size has been increased even more. Both simultaneous reading and writing are possible. The advantage of this option is that the array capacity available to the user is reduced by the capacity of only one disk, although the reliability of data storage is lower than that of RAID 1. In fact, it is a compromise between RAID0 and RAID1, providing a fairly high speed of operation with good data storage reliability . If one disk in the array fails, data can be restored without loss of data. automatic mode. Minimal amount There are 3 disks for such an array.
"Software" implementations of RAID5, built into the south bridges of motherboards, do not have high write speeds, so they are not suitable for all applications.


RAID 5EE

RAID 5EE- an array similar to RAID5, however, in addition to distributed storage of parity codes, the distribution of spare areas is used - in fact, it is used, which can be added to the RAID5 array as a spare (such arrays are called 5+ or 5+spare). In a RAID 5 array backup disk remains idle until one of the main ones fails, while in a RAID 5EE array this disk is shared with the rest of the HDDs all the time, which has a positive effect on the performance of the array. For example, a RAID5EE array of 5 HDDs will be able to perform 25% more I/O operations per second than a RAID5 array of 4 primary and one backup HDD. The minimum number of disks for such an array is 4.


RAID 6

RAID 6- an analogue of RAID5 with a high level of redundancy - information is not lost if any two disks fail; accordingly, the total capacity of the array is reduced by the capacity of two disks. The minimum number of disks required to create an array of this level is 4. The operating speed in the general case is approximately the same as RAID5. Recommended for applications where the highest possible reliability is important.


RAID 50

RAID 50- combining two (or more, but this is extremely rarely used) RAID5 arrays into a stripe, i.e. a combination of RAID5 and RAID0, partially correcting the main disadvantage of RAID5 - low speed data recording due to parallel use several such arrays. The total capacity of the array is reduced by the capacity of two, but, unlike RAID6, such an array can withstand the failure of only one disk without data loss, and the minimum required number of disks to create a RAID50 array is 6. Along with RAID10, this is the most recommended RAID level for use in applications where high performance combined with acceptable reliability is required.


RAID 60

RAID 60- combining two RAID6 arrays into a stripe. The write speed is approximately doubled compared to the write speed in RAID6. The minimum number of disks to create such an array is 8. Information is not lost if two disks from each RAID 6 array fail.

Matrix RAID- technology implemented by Intel in its southern bridges, starting with ICH6R, which allows you to organize several RAID0 and RAID1 arrays on just two disks, while simultaneously creating partitions with both increased operating speed and increased data storage reliability.

JBOD(From English "Just a Bunch Of Disks") - sequential combination of several physical disks into one logical one, which does not affect performance (reliability drops similar to RAID0), but may have different sizes. Currently practically not used.

© Andrey Egorov, 2005, 2006. TIM Group of Companies.

Forum visitors ask us the question: “Which RAID level is the most reliable?” Everyone knows that the most common level is RAID5, but it is not without serious drawbacks that are not obvious to non-specialists.

RAID 0, RAID 1, RAID 5, RAID6, RAID 10 or what are RAID levels?

In this article, I will try to characterize the most popular RAID levels, and then formulate recommendations for using these levels. To illustrate the article, I created a diagram in which I placed these levels in the three-dimensional space of reliability, performance and cost efficiency.

JBOD(Just a Bunch of Disks) is a simple spanning of hard drives, which is not formally a RAID level. A JBOD volume can be an array of a single disk or an aggregation of multiple disks. The RAID controller does not need to perform any calculations to operate such a volume. In our diagram, the JBOD drive serves as a “single” or starting point—its reliability, performance, and cost values ​​are the same as those of a single hard drive.

RAID 0(“Striping”) has no redundancy, and distributes information immediately across all disks included in the array in the form of small blocks (“stripes”). Due to this, performance increases significantly, but reliability suffers. As with JBOD, we get 100% of the disk capacity for our money.

Let me explain why the reliability of data storage on any composite volume decreases - since if any of the hard drives included in it fail, all information is completely and irretrievably lost. In accordance with probability theory, mathematically, the reliability of a RAID0 volume is equal to the product of the reliabilities of its constituent disks, each of which is less than one, so the total reliability is obviously lower than the reliability of any disk.

Good level - RAID 1(“Mirroring”, “mirror”). It has protection against failure of half of the available hardware (in the general case, one of two hard drives), provides an acceptable write speed and gains in read speed due to parallelization of requests. The disadvantage is that you have to pay the cost of two hard drives to get the usable capacity of one hard drive.

Initially, it is assumed that the hard drive is a reliable thing. Accordingly, the probability of failure of two disks at once is equal (according to the formula) to the product of the probabilities, i.e. orders of magnitude lower! Unfortunately, real life- not a theory! Two hard drives are taken from the same batch and operate under the same conditions, and if one of the disks fails, the load on the remaining one increases, so in practice, if one of the disks fails, urgent measures must be taken to restore redundancy. To do this, it is recommended to use hot spare disks with any RAID level (except zero) HotSpare. The advantage of this approach is maintaining constant reliability. The disadvantage is even greater costs (i.e. the cost of 3 hard drives to store the volume of one disk).

Mirror on many disks is a level RAID 10. When using this level, mirrored pairs of disks are arranged in a “chain”, so the resulting volume can exceed the capacity of a single hard drive. The advantages and disadvantages are the same as for the RAID1 level. As in other cases, it is recommended to include HotSpare hot spare disks in the array at the rate of one spare for every five workers.

RAID 5, indeed, the most popular of the levels - primarily due to its efficiency. By sacrificing the capacity of just one disk from the array for redundancy, we gain protection against failure of any of the volume’s hard drives. Writing information to a RAID5 volume requires additional resources, since additional calculations are required, but when reading (compared to a separate hard drive), there is a gain, because data streams from several array drives are parallelized.

The disadvantages of RAID5 appear when one of the disks fails - the entire volume goes into critical mode, all write and read operations are accompanied by additional manipulations, performance drops sharply, and the disks begin to heat up. If immediate action is not taken, you may lose the entire volume. Therefore, (see above) you should definitely use a Hot Spare disk with a RAID5 volume.

Besides basic levels RAID0 - RAID5, described in the standard, there are combined levels RAID10, RAID30, RAID50, RAID15, which different manufacturers interpret each in their own way.

The essence of such combinations is briefly as follows. RAID10 is a combination of one and zero (see above). RAID50 is a combination of “0” level 5 volumes. RAID15 is a “mirror” of the “fives”. And so on.

Thus, combined levels inherit the advantages (and disadvantages) of their “parents”. So, the appearance of a “zero” in the level RAID 50 does not add any reliability to it, but has a positive effect on performance. Level RAID 15, probably very reliable, but it is not the fastest and, moreover, extremely uneconomical (the useful capacity of the volume is less than half the size of the original disk array).

RAID 6 differs from RAID 5 in that in each row of data (in English stripe) has not one, but two checksum block. Checksums are “multidimensional”, i.e. independent of each other, so even the failure of two disks in the array allows you to save the original data. Calculating checksums using the Reed-Solomon method requires more intensive calculations compared to RAID5, so previously the sixth level was practically not used. Now it is supported by many products, since they began to install specialized microcircuits that perform all the necessary mathematical operations.

According to some studies, restoring integrity after a single drive failure on a RAID5 volume composed of SATA drives large volume (400 and 500 gigabytes), in 5% of cases it ends in data loss. In other words, in one case out of twenty, during the regeneration of a RAID5 array to a Hot Spare disk, the second disk may fail... Hence the recommendations of the best RAID drives: 1) Always do backups; 2) use RAID6!

Recently new levels RAID1E, RAID5E, RAID5EE have appeared. The letter “E” in the name means Enhanced.

RAID level-1 Enhanced (RAID level-1E) combines mirroring and data striping. This mixture of levels 0 and 1 is arranged as follows. The data in a row is distributed exactly as in RAID 0. That is, the data row has no redundancy. The next row of data blocks copies the previous one with a shift of one block. Thus, as in standard RAID 1 mode, each data block has a mirror copy on one of the disks, so the useful volume of the array is equal to half the total volume of the hard drives included in the array. RAID 1E requires a combination of three or more drives to operate.

I really like the RAID1E level. For powerful graphics workstation or even for home computer – optimal choice! It has all the advantages of the zero and first levels - excellent speed and high reliability.

Let's now move on to the level RAID level-5 Enhanced (RAID level-5E). This is the same as RAID5, only with a backup disk built into the array spare drive. This integration is carried out as follows: on all disks of the array, 1/N part of the space is left free, which is used as a hot spare if one of the disks fails. Due to this, RAID5E demonstrates, along with reliability, better performance, since reading/writing is performed in parallel from a larger number of drives at the same time and the spare drive is not idle, as in RAID5. Obviously, the backup disk included in the volume cannot be shared with other volumes (dedicated vs. shared). A RAID 5E volume is built on a minimum of four physical disks. The useful volume of a logical volume is calculated using the formula N-2.

RAID level-5E Enhanced (RAID level-5EE) similar to RAID level-5E, but it has more efficient spare drive allocation and, as a result, more fast time recovery. Like the RAID5E level, this RAID level distributes blocks of data and checksums in rows. But it also distributes free blocks of the spare drive, and does not simply reserve part of the disk space for these purposes. This reduces the time required to reconstruct the integrity of a RAID5EE volume. The backup disk included in the volume cannot be shared with other volumes - as in the previous case. A RAID 5EE volume is built on a minimum of four physical disks. The useful volume of a logical volume is calculated using the formula N-2.

Oddly enough, no mention of level RAID 6E I couldn’t find it on the Internet - so far this level is not offered or even announced by any manufacturer. But the RAID6E (or RAID6EE?) level can be offered according to the same principle as the previous one. Disk HotSpare Necessarily must accompany any RAID volume, including RAID 6. Of course, we will not lose information if one or two disks fail, but it is extremely important to start regenerating the integrity of the array as early as possible in order to quickly bring the system out of the “critical” mode. Since the need for a Hot Spare disk is beyond doubt for us, it would be logical to go further and “spread” it over the volume as is done in RAID 5EE in order to get the benefits of using a larger number of disks (better read-write speed and more fast recovery integrity).

RAID levels in “numbers”.

I have collected some of them in a table important parameters almost all RAID levels, so that you can compare them with each other and better understand their essence.

Level ~~~~~~~

Huts- exactly ness ~~~~~~~

Use Disk capacity ~~~~~~~

Production ditel- ness reading ~~~~~~~

Production ditel- ness records ~~~~~~~

Built-in disk reserve ~~~~~~~

Min. number of disks ~~~~~~~

Max. number of disks ~~~~~~~

Exc.

Exc.

Exc.

Exc.

All “mirror” levels are RAID 1, 1+0, 10, 1E, 1E0.

Let's try again to thoroughly understand how these levels differ?

RAID 1.
This is a classic “mirror”. Two (and only two!) hard drives work as one, being a complete copy of each other. Failure of either of these two drives does not result in loss of your data, as the controller continues to operate on the remaining drive. RAID1 in numbers: 2x redundancy, 2x reliability, 2x cost. Write performance is equivalent to that of a single hard drive. Read performance is higher because the controller can distribute read operations between two disks.

RAID 10.
The essence of this level is that the disks of the array are combined in pairs into “mirrors” (RAID 1), and then all these mirror pairs, in turn, are combined into a common striped array (RAID 0). That is why it is sometimes referred to as RAID 1+0. Important point– RAID 10 can only combine an even number of disks (minimum 4, maximum 16). Advantages: reliability is inherited from the “mirror”, performance for both reading and writing is inherited from “zero”.

RAID 1E.
The letter "E" in the name means "Enhanced", i.e. "improved". The principle of this improvement is as follows: the data is “stripped” in blocks across all disks of the array, and then “striped” again with a shift to one disk. RAID 1E can combine from three to 16 disks. Reliability corresponds to the “ten” indicators, and performance becomes a little better due to greater “alternation”.

RAID 1E0.
This level is implemented like this: we create a “null” array from RAID1E arrays. Therefore, the total number of disks must be a multiple of three: a minimum of three and a maximum of sixty! In this case, we are unlikely to get a speed advantage, and the complexity of the implementation may adversely affect reliability. The main advantage is the ability to combine a very large (up to 60) number of disks into one array.

The similarity of all RAID 1X levels lies in their redundancy indicators: for the sake of reliability, exactly 50% of the total capacity of the array disks is sacrificed.

RAID array (Redundant Array of Independent Disks) - connecting several devices to increase performance and/or reliability of data storage, in translation - a redundant array of independent disks.

According to Moore's law, current productivity increases every year (namely, the number of transistors on a chip doubles every 2 years). This can be seen in almost every computer hardware industry. Processors increase the number of cores and transistors, while reducing the process RAM increases frequency and throughput, memory solid state drives increases wear resistance and reading speed.

But simple hard drives (HDDs) have not advanced much over the past 10 years. As the standard speed was 7200 rpm, it remains so (not taking into account server HDDs with revolutions of 10,000 or more). Slow 5400 rpm is still found on laptops. For most users, in order to increase the performance of their computer, it will be more convenient to buy an SDD, but the price for 1 gigabyte of such media is much higher than that of a simple HDD. “How to increase the performance of drives without losing a lot of money and volume? How to save your data or increase the security of your data? There is an answer to these questions - a RAID array.

Types of RAID arrays

On this moment The following types of RAID arrays exist:

RAID 0 or "Striping"– an array of two or more disks to improve overall performance. The raid volume will be total (HDD 1 + HDD 2 = Total volume), the read/write speed will be higher (due to splitting the recording into 2 devices), but the reliability of information security will suffer. If one of the devices fails, all information in the array will be lost.

RAID 1 or "Mirror"– several disks copying each other to increase reliability. The write speed remains at the same level, the read speed increases, reliability increases many times over (even if one device fails, the second will work), but the cost of 1 Gigabyte of information increases by 2 times (if you make an array of two hdds).

RAID 2 is an array built on disks for storing information and error correction disks. The number of HDDs for storing information is calculated using the formula “2^n-n-1”, where n is the number of HDD corrections. This type is used when large quantities HDD, the minimum acceptable number is 7, where 4 is for storing information, and 3 is for storing errors. The advantage of this type will be increased performance compared to a single disk.

RAID 3 – consists of “n-1” disks, where n is a disk for storing parity blocks, the rest are devices for storing information. Information is divided into pieces smaller than the sector size (divided into bytes), well suited for working with large files, the reading speed of small files is very low. Characterized by high performance, but low reliability and narrow specialization.

RAID 4 is similar to type 3, but is divided into blocks rather than bytes. This solution was able to correct the low reading speed of small files, but the writing speed remained low.

RAID 5 and 6 - instead of a separate disk for error correlation, as in previous versions, blocks are used that are evenly distributed across all devices. In this case, the speed of reading/writing information increases due to parallelization of recording. Minus of this type is long-term recovery of information in the event of failure of one of the disks. During recovery it goes very high load to other devices, which reduces reliability and increases the failure of another device and the loss of all array data. Type 6 improves overall reliability but reduces performance.

Combined types of RAID arrays:

RAID 01 (0+1) – Two Raid 0s are combined into Raid 1.

RAID 10 (1+0) – RAID 1 disk arrays, which are used in type 0 architecture. It is considered the most reliable data storage option, combining high reliability and performance.

You can also create an array from SSD drives . According to 3DNews testing, such a combination does not provide a significant increase. It is better to purchase a drive with a more powerful PCI or eSATA interface

Raid array: how to create

Created by connecting through a special RAID controller. At the moment there are 3 types of controllers:

1. Software – software an array is emulated, all calculations are performed by the CPU.
2. Integrated – mainly common on motherboards (not the server segment). A small chip on the mat. board responsible for emulating the array, calculations are performed through the CPU.
3. Hardware – expansion card (for desktop computers), usually with PCI interface, has its own memory and computing processor.

RAID hdd array: How to make it from 2 disks via IRST

Data recovery

Some data recovery options:

1. If Raid 0 or 5 fails, the RAID Reconstructor utility can help, which will collect the available drive information and rewrite it to another device or media in the form of an image of the previous array. This option It will help if the disks are working properly and the error is software.
2. For Linux systems mdadm recovery is used (a utility for managing software Raid arrays).
3. Hardware recovery should be performed through specialized services, because without knowledge of the controller’s operating methods, you can lose all data and it will be very difficult or even impossible to get them back.

There are many nuances that need to be taken into account when creating a Raid on your computer. Basically, most options are used in the server segment, where data stability and security is important and necessary. If you have questions or additions, you can leave them in the comments.

Have a great day!

Hard drives play a very important role in our computer. All information is stored on them. I don’t want to lose everything overnight due to hard drive failure. And they, as you know, also have their own MTBF limit. Surely, many of you have heard about certain RAID arrays. They are made to speed up the computer and for data security. Let's talk more about this.

What is RAID and what is it for?

RAID is a disk array of several hard drives. In practice, a RAID array is a system consisting of two hard drives connected to a motherboard that supports the creation of arrays (or to a RAID controller). What is a RAID controller? A device that controls your array and related processes. They are usually used on server machines. For ordinary users, such a toy is of little use - it is not cheap and ineffective, given the amount of information processed by an ordinary computer. When creating a RAID array, the hardware of your computer will not change. Programmatically, all work with the raid is carried out in bios, that is, nothing labor-intensive.

SCSI RAID: difference from a classic array

SCSI is an interface, a physical type of device connection. It differs from the usual IDE or SATA interfaces, first of all, in a different operating algorithm, which provides higher speed, and in an inflated price relative to the latter. It has become widespread on large-scale server machines; it is rarely installed among ordinary computers.

Installing a RAID array

1. We find a motherboard that supports raid arrays or SCSI RAID.
2. We take two absolutely identical disks, connect.
3. Go to bios (depending on the motherboard model).
4. SATA Configuration parameter, set RAID.
5. While the computer is booting, press Ctrl + I.
6. Setting up a raid.

Ready! Important: when creating RAID arrays, all information from the disks is deleted!

Types of arrays

• RAID 0 - disk array to improve performance.
• RAID 1 is a “mirror” disk array.
• RAID 2 - arrays that use Hamming code.
• RAID 3 and 4 are striped disk arrays with a dedicated parity disk.
• RAID 5 - striped disks with a non-dedicated parity disk.
• RAID 6 - striped disks with 2 independent parities.
• There are also raids 10, 50, 60. But these are too complex designs.

Let's take a closer look at the two most popular versions of raid arrays. These are, respectively, RAID 0 and RAID 1. What is RAID 0 for? It's not that complicated. The principle of operation of the array is the parallel operation of different physical devices, issued to the system as one. That is, this directly increases the speed of the system, just imagine: your raid 0 array includes two disks. You are recording 10 gigabytes of data. If you had not created an array, you would have to write them to a specific disk, while the second one would necessarily be idle. In the case of a raid 0 array, your data is divided byte-by-byte into several streams, and is also written to the media randomly. That is, one movie can be stored on two physical devices at the same time, and only 30% of its “weight” will be on one. The disadvantage of RAID 0 is the lack of fault tolerance. Moreover, if one disk fails, then you will not be able to recover the data from the second one either.

Now let's talk about RAID 1. In the case of this array, you will have to use several additional disks for “mirroring”. If you have only two disks in the array, then it looks like this: you work with disk number 1, and the computer duplicates all your actions for disk 2. In the event of a device failure, all your data will be safe and sound on the duplicate disk. Safe, no doubt. The downside of raid 1 is the loss of performance.

You now know why you need a RAID array, all that remains is to decide what suits you best. Data security or productivity gains? Everyone's personal business!