We are going to extend the last Storage-Tier with 43 7.2k Drives (ST9100640SS). The primary aim is capacity, secondary is speed.
- Te used controller is a MegaRaid 9285W-8e featuring a LSI2208-Chipset+1GB Cache
- As our hole SAN is completely mirrored we decided to configure the Drives in Raid5-Stripes.
- Because we have to reconfigure the SAN online we can put together a maximum of 10 Drives in a singel Raidset (put in 10 drives, configure, migrate date from old drives to new, remove old drives, put in another set of new drives and so on)
- We want to use at least 1 Drive as Hotspare!
- Our san spreds datablocks across all Raidsets within a Tier theoreticaly accumulating the Performance of all Raidsets in best case.
What Raid-size should we choose? We are debating Sets of 7 x 6 Drives + 2 HS, 5 x 8 Drives + 3 HS or 4 x 10 Drives + 3 HS.
For all 3 configurations the theoretical MTTDL / propability of Dataloss is acceptabel
We benchmarkt all three sizes. The relativ Raidset-Performance is exactly what we theoreticaly calculated ( Handling the 10Drive-Raidsetiops as 100% we reached: 10Drive Raidset: 100% / 8 Drive Raidset: 76% (75 calculated) / 6 Drive Raidset 61% (60% calculated) )
Of corse 4 Sets of 10 Drives gives the highest netto-capacity
7 Sets of 6 Drives benefits in a slightliy higher (~5%) accumulated Performance
We are trending to use the 4 x 10 Drives configuration but our reseller continously jells us to use the 6drive-set configuration.
Now im a little bit helpless.
Can someone give me a hint?