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What type of RAID would you recommend for a single storage segment across 16 of 900 GB 10K SAS SFF disks on an EMC VNX 5100 storage unit? Disk 17 is a hot-spare.

RAID 10, RAID 50 or something else?

Unformatted capacity is 14.4 TB, but we will not be using more than 4 TB of space. Storage will primarily be used for Hyper-V VHD's.

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What RAID level meets your storage needs and objectives? Which ever one it is, set it up that way. –  joeqwerty Oct 3 '12 at 19:37

3 Answers 3

RAID 6 or RAID 10. RAID 10 is a bit of a capacity waste, and RAID 6's random write penalty is completely hidden behind the write cache. I know you only think you'll need 4TB, but there's no reason to waste.

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Based on the little info you provide, I would suggest RAID 10.

Mostly because you really don't need much disk space and because rebuilding a failed disk that are almost 1TB big will take forever (Raid 50).

The chances of loosing both disk in a pair is already very slim...spread across 8 pairs...that's nearly impossible.

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+1 for RAID 10. Mirroring is always better than unless you're too poor to afford more/larger disks and you don't care (at all) about performance. –  bahamat Oct 3 '12 at 21:54
    
@bahamat This is common knowledge for DAS, but most halfway decent SANs have between 12 and 48GB of write cache. This completely negates the R6 write penalty. Yes, rebuilds will be longer in a R6 (or R60), but they are not as dangerous are a R5 rebuild. I completely agree that RAID 5 is a bad idea, but RAID 6 is probably the best choice given the amount of cache that normally comes in the VNX 5000 series. –  MDMarra Oct 12 '12 at 17:07

RAID 10 for best performance but you lose 50% to fault tolerance, balanced approach is RAID 50, good performance, I do not recommend RAID-5 or even worse RAID-6 beacuse of bad write performance.

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This is common knowledge for DAS, but not the case for SAN. R6's write penalty is masked by large amount of write cache on the SAN and read performance between an R6 and R10 should be very similar. –  MDMarra Oct 12 '12 at 17:08

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