The term "RAID" was proposed in 1987 by Petterson (David A. Patterson), Gibson (Garth A. Gibson) and Katz
(Randy H. Katz) as an abbreviation for the English Redundant Array of Inexpensive Disks ("redundant array of inexpensive disks").
In their presentation, they argued for their invention with the relatively low cost of an array of cheap disks
designed for personal computers, in comparison with high-capacity disks, which they called
«SLED» (Single Large Expensive Drive).
Later, the interpretation of the term changed to Redundant Array of Independent Disks (redundant array of independent Disks
(independent) disks), because expensive server disks were often used in arrays.
RAID 0 (striping — "striping") is a disk array of two or more hard drives without redundancy.
The information is divided into fixed-length data blocks and written to both/several disks in turn, that is
one block to the first disk, and the second block to the second disk, respectively.
The level is based on the division of information into blocks with simultaneous recording of different blocks on different disks.
The technology significantly increases the speed of reading and writing, while the user can use the total
the volume of all drives. There is one drawback — fault tolerance tends to zero, i.e. to restore the damaged
HDD/SSD will no longer be possible.
To implement such a solution, you need at least 2 disks.
RAID 1 (mirroring— is an array of two disks that are complete copies of each other.
Not to be confused with RAID 1+0 (RAID 10), RAID 0+1 (RAID 01) arrays, which use more
complex mirroring mechanisms.
This method is already based on the complete duplication of data into several media.
The principle is steep and reinforced concrete in terms of reliability, but when using two disks with a capacity of 2 TB, you
you get only one worker. The second one becomes invisible to the system — only to the RAID controller.
The process also does not provide any advantages in speed, but fault tolerance increases several times.
If one of the HDD/SSD has been ordered to live for a long time, its full cast is on the second medium.
The processes of writing, deleting and copying occur in parallel. There is one caveat from this: the information has been erased
from one HDD, it disappears automatically on the second one.
To implement such a solution, you need at least 2 disks.
RAID 2 arrays of this type are based on the use of Hamming code. Disks are divided into two groups:
for data and for error correction codes, and if the data is stored on two disks, then it is necessary to store correction codes
at least three disks. The total number of disks in this case will be equal to three disks. The data is distributed across the disks
intended for storing information in the same way as in RAID 0, that is, they are divided into small blocks according to the number of disks.
The remaining disks store error correction codes, according to which, in case of failure of any hard disk, it is possible
information recovery.
To implement such a solution, you need at least 3 disks.
In a RAID 3 disk array, data is split into chunks smaller than a sector (split into bytes) and distributed
on two disks. Another disk is used to store parity blocks.
This unified format for organizing a disk array uses striping and allocates one disk from an available pool
storage devices for storing parity information, which is responsible for checking the integrity by determining
whether data was lost or overwritten when it was directly moved from one storage location to another
or at the time of transfer between computers.
To implement such a solution, you need at least 3 disks.
RAID 4 is similar to RAID 3, but differs from it in that data is split into blocks, not bytes. Thus,
it was partially possible to "defeat" the problem of low data transfer rate of a small volume. The recording is being made
it is slow due to the fact that the parity for the block is generated during recording and is written to a single disk.
To implement such a solution, you need at least 3 disks.
RAID 5 is a disk array with alternating data blocks and parity control.
The main disadvantage of RAID levels from 2nd to 4th is the inability to produce parallel
write operations, since a separate control disk is used to store parity information.
RAID 5 does not have this disadvantage. Data blocks and checksums are cyclically written to all disks
of course, there is no asymmetry in the disk configuration. The technology is considered one of the most widespread and safe,
because it works on the principles of parity and alternation. To create a fifth Raid, you must have at least 3 disks.
During recording, the data is divided into blocks, with a special condition: to one of the disks, called a block
parity (Parity Drive/PD) information is written for further recovery. In case something went wrong by
the fault of the user, or the obsolescence of the drives as a whole.
The convenience of RAID 5 is that it can be implemented both hardware and software using the appropriate utilities
supplied with the OS. However, any intelligent specialist will say that the hard-core option is much safer.
To implement such a solution, you need at least 4 disks.
RAID 6 is an array of four or more disks with P+Q or DP parity checking, designed to protect
from data loss when two hard drives in the array fail at once. This reliability is achieved by
due to reduced performance and reduced capacity, two steps are needed to restore information
computing operations, and two disks in the array are not used to store data, but to control them
integrity and failure recovery.
In many ways, this technology duplicates the features of RAID 5, but the data for recovery is copied to two backup media at once.
The second parity disk is, in fact, a duplicate link, to be sure. The principle of its operation is based on the Reed-Solomon code,
and therefore the second drive is labeled as Q or RS.
Thanks to this principle, the server owner can painlessly transfer the untimely death of a pair of HDD/SSD at once.
That's just for the implementation of RAID 6, you will need 4 disks already.
RAID 7 is a registered trademark of Storage Computer Corporation, a separate level
RAID is not. The structure of the array is as follows: two disks store data, one disk is used for storage
blocks of parity. Writing to disks is cached using RAM, the array itself requires mandatory
UPS; in case of power outages, data corruption occurs.
To implement such a solution, you need at least 2 disks.
RAID 10 (RAID 1+0) is a mirrored array in which data is written sequentially to several disks, as in RAID 0.
This architecture is a RAID 0 array, the segments of which are RAID 1 arrays instead of individual disks.
Accordingly, an array of this level must contain at least 4 disks (and always an even number). RAID 10 combines into
high fault tolerance and performance.
This technology combines the advantages of RAID 1 and RAID 0 in virtualization mode, which provides high speed
recovery, excellent reliability and performance.
RAID 10 is a nested RAID type that combines RAID 1 and RAID 0, hence its name. Many professionals
they prefer to write it as RAID 1+0. The array first splits the data into blocks (RAID 0), and then creates for them
mirroring on separate disks (RAID 1). Remember, this is not the same as RAID 0 + 1, which works
in the opposite direction, first creating a mirror image of the data, and then splitting it into blocks.
To implement such a solution, you need at least 4 disks.
This configuration takes all the advantages of RAID 5 (parity) and RAID 0 (striping) to improve performance without
reducing protection indicators. But only if you have 6 disks or more.
RAID organization allows you to survive a breakdown of up to 4 disks if they are hanging in a separate RAID 5 array.
To implement such a solution, you need at least 6 disks.
RAID 60 (also called RAID 6+0) is a combined set of RAID 0 and RAID 6 arrays, offering the user
improved performance and processing speed of the array data. This combination has not been widely used,
but it has some advantages, among which it is especially possible to highlight the possibility of maintaining operability
(no delays in calculating and writing a large number of parity bits) while increasing the total volume in parallel
spaces.
Striping ("striping") helps to increase throughput and performance without adding additional
disks are attached to each RAID 6 set, which, in turn, reduces data availability. RAID 60 increases performance
RAID 6, despite the fact that RAID 60 is noticeably slower than RAID 50, especially in terms of "writing" data.
To implement such a solution, you need at least 8 disks.
The Dell PowerEdge server management solution is based on an integrated Lifecycle Controller (LCC).
LCC is a lightweight operating system that runs from iDRAC to receive instructions from the systems
management.
It also serves as a direct point for updates and helps to perform automated tasks in
in accordance with the instructions for creating and maintaining workable servers.
The iDRAC controller is hardware integrated into the server motherboard and,
like other BMC solutions, has its own processor, memory, network connection and access to the system bus.
iDRAC provides remote access to the system console (keyboard and screen), allowing access to the BIOS
systems over the Internet when the server is restarted. The main functions of iDRAC include power management, access to
virtual media and remote console capabilities. These functions give administrators the ability to customize
the computer is as if they were sitting in front of a local console.