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11 Dell PS Series Storage: Choosing a Member RAID Policy | TR1020 | v 4.7
Relative performance by RAID policy
Key Observation: RAID 10 still offers the best random performance.
Another factor to consider, when comparing the performance of different RAID levels is the performance
impact of an individual RAID set operating in a degraded mode.
Degraded: When a disk in a RAID set fails and there is no spare disk to replace it, the set is still functional,
but degraded. Another disk failure (except in RAID 6) could result in a complete loss of data in the set.
 With RAID 6, there is moderate impact on read and write performance on a heavily loaded system.
The impact difference is negligible compared to RAID 5 or 50, even with two parity calculations to
reconstruct the data. However, RAID 6 can survive the simultaneous failure of any two disks in a set.
 With RAID 10, there is only minimal impact on read performance in the RAID 1 mirror set that has
experienced the failure. There is negligible impact on the overall read performance.
 With RAID 5/RAID 50, there is moderate impact on read performance and random write performance,
due to the parity reconstruction overhead.
Degraded Reconstructing: When a disk in a RAID set fails and a spare disk is available, the amount of time
needed to reconstruct the data from parity information must be considered in the context of both heavy and
light workloads.
 With RAID 6, data reconstruction is equal to RAID 5 or RAID 50 with a single disk failure. With a
double disk failure, RAID 6 can involve slightly more overhead than a RAID 5 or RAID 50 because
two parity calculations must be performed. This slight difference in overhead is outweighed by the
additional level of protection RAID 6 offers. RAID 6 will continue to protect the RAID set should one
occur whereas other RAID types will not.
RAID 6 RAID 10 RAID 50 RAID 5
50/50 Random
81% 151% 100% 106%
50/50 Seq
82% 99% 100% 92%
0%
20%
40%
60%
80%
100%
120%
140%
160%