08-12
29

The Common RAID levels—RAID 5

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AuthorEASEUS   Category Basic Computing Guide   Comments0   Post Time 2008-12-29 03:22:27 -0500

RAID 5 uses block-level striping with parity data distributed across all member disks. It has achieved popularity due to its low cost of redundancy. Advantage can be shown by comparing the number of drives needed to achieve a given capacity.


RAID 5 will be poor performance when faced with a workload which includes many writings. This is because parity must be updated on each write, requiring read-modify-write sequences for both the data block and the parity block. More complex implementations may include a non-volatile write back cache to reduce the performance impact of incremental parity updates.


The read-modify-write cycle requirement of RAID 5's parity implementation penalizes random writes by as much as an order of magnitude compared to RAID 0.The read performance of RAID 5 is almost as good as RAID 0 for the same number of disks. Except for the parity blocks, the distribution of data over the drives follows the same pattern as RAID 0. The reason why RAID 5 is slightly slower is that the disks must skip over the parity blocks.

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