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RAID levels
No RAID calculation– —the required archive size without calculating the number of disks will be shown in the results.
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JBOD (Just a Bunch of Disks) – is a method of attaching a set of independent disks to a RAID controller that provides the same access to each disk as the connection to a regular adapter.
Features:
- JBOD is not
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- a RAID level because it does not improve performance and/or reliability
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- disk system performance is limited by the speed of a single disk
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- the disk system is not protected
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- . Failure of one of the disks leads to the loss of data for the entire array
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- for JBOD disk space is 100% utilized because the entire capacity of the available disks in the array is suitable for storing data.
For Possible use case: storing of a video archive there may be interesting scenario when several . Several physical disks are not combined into one large logical disk, but work independently (if one physical disk is full, recording on the next one starts, etc.). In this case, the failure of one disk will not lead to the loss of the entire video archive, since the data on the properly functioning disks will remain available. But this only applies to small systems due to the limited performance of JBOD.
RAID-0 – is ahigh performance striped disk array without fault tolerance.
When using RAID-0, information is split into fixed-length blocks of data, which are written in turn to each disk. This ensures maximum performance since multiple disks read/write their chunk of data at the same time.
Features:There
- there is no data redundancy in RAID-0, so the failure of one of the
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- disks leads to the loss of data for the entire array
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- disk space is 100% utilized as all available disk capacity in the array is suitable for storing data
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- the
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- minimum number of disks to build an array is 2.
Typically, RAID-0 is used for tasks where fast access to large amounts of temporary data (which can be reloaded in case of failure) is required, such as data caching, video/audio post-processing, etc.
RAID-1 – is a fault-tolerant disk array with data mirroring (duplication).
Each disk has a duplicate in RAID-1, the information is recorded synchronously to the original and the duplicate. Therefore, the increase in performance occurs only when reading, the write speed is limited by the speed of a single disk.RAID-1 has
Features:
- a high degree of reliability
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- . If one of the disks fails, a copy of its data remains available on the duplicate disk
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- ;
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- the usable disk space is 50% of the available disks in the array (the number of redundant disks equals the number of
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- "usable" disks)
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- the
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- number of disks is always even, the minimum number of disks for building an array is 2.
RAID-1 is often used in servers to combine two system drives in a mirror due to its simplicity and reliability. For storing of a video archive RAID-1 is advisable to use only in very small systems, since this RAID level has a low write speed and the lowest efficiency of disk space utilization with three or more disks.
RAID-10 – is a fault-tolerant striped and mirrored disk array.
When using RAID-10, one essentially create a RAID-0 array from multiple RAID-1 arrays (with two disks for each RAID-1 subarray). Thus, RAID-10 combines both the speed advantages of RAID-0 and the high reliability of RAID-1 (one disk failure in each RAID-1 subarray is allowed).
Features:The
- the usable disk space is 50% of the available disks in the array (the number of redundant disks equals the number of
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- "usable" disks)
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- the
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- number of disks is always even, the minimum number of disks for building an array is 4.
Typically, RAID-10 is used for working with databases where both high performance and reliability are required. It is rarely used for storing a video archive due to the low efficiency of using disk space. However, in cases where the performance and/or reliability of other RAID levels is not enough, the use of RAID-10 for a video archive may be appropriate (in practice, 4 disks are used to build a RAID-10, and when a larger capacity is required, more economical RAID-50 or RAID-60 are preferable, they are faster than RAID-5/RAID-6 while maintaining reliability).
RAID-5 – is a fault-tolerant striped disk array with one checksum.
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RAID-5 has a basic level of reliability, one disk failure is allowed. But it should be remembered that this This triggers a lengthy recovery process (rebuild) of the RAID array, which dramatically increases the load on the disks. This in turn can provoke the failure of the second disk and lead to a complete loss of data. Despite the fact that RAID-5 is inferior in reliability to RAID-1/RAID-10, this is enough for many tasks.
The main advantage of RAID-5 is the most efficient use of disk space among all fault-tolerant RAID arrays. The usable storage capacity of the disk space ranges from 67% and more, depending on the number of disks in the array (only 1 redundant disk is required for any number of “usable” "usable" disks). The minimum number of disks to build an array is 3.
RAID 5 is widely used for a great variety of tasks, including storing a video archive for a not large systems.
RAID-6 – is a fault-tolerant striped disk array with two checksums.
RAID-6 is an evolution of the RAID-5 level, data blocks and checksums are also written cyclically across all disks, but it uses two sets of checksums (only one set is used in RAID-5). This reduces performance compared to RAID-5, but provides better fault tolerance. It is worth noting that the The use of modern RAID controllers with write cache reduces the difference in performance between RAID-5 and RAID-6 to a minimum.
Features:
- RAID-6 has a high level of reliability; failure of any two disks is allowed
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- the usable storage capacity in RAID-6 ranges from 50% and more, depending on the number of disks in the array (only 2 redundant disks are required for any number of
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- "usable" disks). Thus, disk space efficiency in RAID-6 is worse than in RAID-5, but better than in RAID-1/RAID-10 when the number of disks in the array is more than four. The minimum number of disks to build an array is 4.
RAID-6 is widely used in data storage systems where maximum transactional performance is not required, in particular, RAID-6 is the best option for storing a video archive in most cases (in terms of performance/reliability).
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For RAID arrays with combining disks into a single logical space (such as RAID-0, RAID-10, RAID-5, RAID-6) an increase in the number of disks, on the one hand, improves performance (due to parallelization of write and read operations), and on the other hand, it can reduce fault tolerance (all array data may be lost in a bad scenario, so the more disks in an array, the more data may be lost). Such arrays include RAID-0, RAID-10, RAID-5, RAID-6.
In the case of RAID-5/RAID-6, the situation is also complicated by the fact that an increase in the capacity and number of disks in the array leads to an increase in the recovery time of the RAID array (rebuild). The recovery process after a failure of one of the disks is always accompanied by an increase in the load on the remaining healthy disks, a decrease in overall performance, etc. Therefore, a too long rebuild period (which can take, for example, more than a week) increases the risk of another or more failure disks, which will lead to a complete loss of all data.
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If more than 16 disks are used on the server, it is recommended to add at least 1 hot spare disk. If more than 34 disks are used — add used—add at least 2 hot spare disks.
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