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RAID 50 (RAID 5+0)

RAID 50 is a nested or hybrid RAID level. Whilst RAID was originally envisaged as a method of using multiple hard disk drives to create a larger single "disk", to add some data security, or a combination of both (e.g. RAID5), the disks that are used to form a RAID can themselves be individual RAID arrays. This is the basis of nested RAID configurations. RAID50 (aka RAID5+0) is a combination of RAID 5 with its balance of performance vs redundancy with RAID 0 and its high performance

Put simply, a RAID 50 array is a RAID 0 array, but rather than being built from individual hard disk drives, it comprises a number of RAID 5 arrays.

RAID 50 data recovery

RAID 50 is vulnerable to any one of its composite RAID 5 arrays failing. This means that any two hard disk drives in a single RAID 5 array failing will result in the entire RAID 50 becoming inaccessible.

The recovery of data from a RAID50 is not a frequent requirement, these type of arrays are typically used in well protected environments with additional data protection from backup and tape archiving. If one RAID5 array does fail and cannot be fully recovered this does mean that there will be data loss evenly distributed throughout the entire RAID0 array.

As with any RAID there is a point at which the array will cease to operate, in the case of RAID 50 if two disk fail in any of the RAID 5 arrays then the entire RAID will cease to operate and a data recovery operation might be required. As RAID50 is a hybrid of RAID5 and RAID0 the data recovery process is a hybrid of that for each of these RAID levels.

Failed or unreadable sectors

As with other RAID levels the incidence of bad sectors on any individual hard disk drive usually results in access to the failing unit being denied. In any part of a RAID50 array having one disk taken out of the equation will result in that part of the array continuing in degraded operation.

Under normal circumstances failures can be survived and failing disks swapped out with no system down time nor reduction in data availability. If, however, multiple failures occur simultaneously the entire RAID will stop working. The data recovery process must first secure all data from the fully working drives and then deal with the failing ones to secure all available data from them before they fail completely. To achieve a complete recovery each composite RAID5 array must be recovered in its entirety, any loss will be reflected as a loss within the RAID50 array.

Failed hard disk drives

If, rather than sectors becoming unreadable, there are hardware errors resulting in hard drives becoming inaccessible, and any RAID5 element goes off-line, then the RAID50 will no longer be operational. In most instances it will not be the case that two or more hard drives have crashed beyond hope, it is more often the case that one has failed completely and caused a destabilisation of the electronics in an erroneous report that other drives have failed. Even if two or more hard drives have failed the likelihood is that enough of the individual devices will be recoverable for the RAID data recovery to be a 100% success.

Last Updated (Thursday, 18 June 2009 15:41)

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