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How mutch Drives in Raid5?

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Good morning!

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?

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We are using Fujitsu JX40 DAS-Boxes. As Fujitsu only puts 1TB-Drives on the compatibility-list we would, according to our reseller, lose waranty and compromise our service/support-agreement. Thats why 1TB .-(

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