Redundant array of independent disks (RAID) is a storage technology that balances data protection, system performance, and storage space by determining how the storage system distributes data. Many different ways of distributing data have been standardized into various RAID levels. Each RAID level offers a trade-off of data protection, system performance, and storage space. For example, one RAID level might improve data protection but reduce storage space. Another RAID level might increase storage space but also reduce system performance.
Various RAID combinations provide different levels of protection against data loss, capacity, and speed. The ReadyDATA supports the following RAID levels:
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RAID 0 (striped disks) distributes data across several disks in a way that gives improved speed and no lost capacity, but all data on all disks is lost if any one disk fails. Although such an array has no actual redundancy, it is customary to call it RAID 0.
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RAID 1 (mirrored disks) duplicates data across two disks in the array, providing full redundancy. Two disks each store exactly the same data, at the same time, and at all times. Data is not lost as long as one disk survives. Total capacity of the array equals the capacity of the smallest disk in the array. At any given instant, the contents of both disks in the array are identical.
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RAID 5 (striped disks with single parity; in a ZFS system also referred to as RAIDz1) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk.
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RAID 6 (striped disks with dual parity; in a ZFS system also referred to as RAIDz2) can recover from the loss of two disks.
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RAID 10 (or 1+0) uses both striping and mirroring. "01" or "0+1" is sometimes distinguished from "10" or "1+0": a striped set of mirrored subsets and a mirrored set of striped subsets are both valid, but distinct, configurations.
A RAID set with redundancy continues to function without interruption when one (or possibly more, depending on the selected RAID level) disks of the array fail, although the array is then vulnerable to further failures. When you replace a bad disk by a new one, the array is rebuilt while the ReadyDATA continues to operate normally. The ReadyDATA supports high availability, allowing you to hot-swap disks without powering down.
Select the RAID level based on the number of disks and protection level that you want to use for the volume:
|
RAID Level |
Number of Required Disks |
Redundancy |
|
RAID 0 |
1 or more |
None |
|
RAID 1 |
2 only (more disks are not supported in RAID 1) |
Supported |
|
RAID 5 |
3 or more |
Supported for 1 disk |
|
RAID 6 |
4 or more |
Supported for 2 disks |
|
RAID 10 |
4 or more, but an even number |
Supported for all disks |
Note: Although a RAID system can be used to back up data from other disks or another array, RAID is not meant to be an alternative or substitute for backing up data. Data might become damaged or destroyed without harm to the disk or disks on which it is stored. For example, part of the data might be overwritten by a system malfunction; a file might be damaged or deleted by a user error or malice, and not noticed for days or weeks; and, of course, the entire array is at risk of physical damage.