Vol 128 Issue 3 2008-10-17 Article 20444 from section "Sun Disk"

Increasing Reliability for Storage Arrays

Many users have chosen either RAID 5 or RAID 1+0 for their data
storage needs. While both of these RAID algorithms provide increased
data availability, they are not without their disadvantages:

- RAID 5 - only able to sustain a single drive failure.

- RAID 1+0 - 50% of the available storage capacity is used for

These disadvantages are exacerbated as disk drive capacity increases.
With larger disks, the RAID 1+0 implementation becomes increasingly
costly. A blueprint by Said A. Syed describes using Raid 6 on the Sun
StorageTek 6140 Array and concludes,

"RAID 6 provides protection against two consecutive drive failures by
using two independent parity calculations. Sun Microsystems takes
advantage of the better performing P+Q algorithm implementation of
RAID 6 and uses dedicated processors for RAID computations on
intelligent RAID controllers in the StorageTek 6140 arrays for
improved performance.

RAID 6 offers highly available storage for applications and
implementations requiring extremely high fault tolerance while
keeping cost down and performance at an acceptable level during
normal circumstances. If best practices are followed, a RAID 6 disk
group is capable of performing at rates very close to RAID 5 with a
slightly higher cost. RAID 6 is also capable of providing reliability
close to RAID 1+0 at a fraction of the cost. "

Details at

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