On 1/4/2013 12:41 PM, Eric Lehti wrote:
I am considering possibility of RAID 6 on our production POWER 7 8202.
Currently it is RAID 5.
Consider carefully. Testing shows for workloads that are approximately
65% READ (so 35% write), you need approximately 20% more disk units than
if RAID5 was used to achieve similar disk response times with all drives
working. If your workload is similar to most customers, you are
probably 65% (or more) WRITES, and then more even drives would be needed.
Beauty of RAID6 is no performance penalty when a single drive has
failed. No noticeable impact after the failed drive has been replaced
and rebuild is occurring either.
Changing from RAID5 to RAID6 requires ending parity protection and
restarting it. (Don't forget to backup before starting this!) The type
of disk controller, disk unit size, and number of drives per controller
(or pair of controllers) determine how long it will take. Feature 5805
IOAs with 24 139G drives might take 6-6.5 hours to start RAID6.