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I see there are both 10K and 15K SCSI available for our Dell PowerEdge 2950. We need to order more 73GB drives. Can we mix drives of different speeds?

Does anyone object to using refurbished drives, as long as we have extras on hand when running RAID 5?

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You should remove the second question about refurbed drives. It is entirely subjective and will probably cause your question to be closed, per the faq. If you edit it soon, then your question will probably remain open. –  MDMarra Dec 9 '11 at 20:35

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You can, but you shouldn't mix rotational speed, since it has performance implications. In a RAID set, you need to be able to write data across all disks. If some are spinning at 10k and others at 15k, you're going to be waiting for the 10k disks to catch up. This could actually perform worse than just having all 10k of the same model in certain situations.

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Very interesting. Could you please give an example where the mix could perform worse than having only 10k? –  Mircea Vutcovici Dec 9 '11 at 20:39
    
@MirceaVutcovici It's not as much about 10k vs 15k as it is about the custom firmware and optimization that Dell and other vendors do to the disks that they sell. By mixing 15k and 10k, you guarantee that you'll have different firmware which negates these benefits. At the best case it's no performance increase. At the worst it's a decrease. In very rare cases, I've even heard of this causing disks to be marked as failed when they're not. I edited my answer to be more clear that it's more about having the same model than it is about having the same rotational speed. –  MDMarra Dec 9 '11 at 20:41
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But why would be an advantage to have the same model? Even Dell is replacing the disks with different brands than the original ones. RAID should work with any disks that are accepted by the manufacturer of the RAID controller. For me it seems more sense to use different brands or models that are of the same type, than to use the same brand and model. In this way I can lower the chances for them to fail at once. –  Mircea Vutcovici Dec 9 '11 at 23:04

Can you mix spindle speeds? Sure, if you have a reasonably modern RAID controller (2950 should be no problem) or if you're using software RAID. The caveat is the array will be limited mainly by the lowest speed drives it has.

Should you use refurbished drives? Only if they come with a warranty equal to (or better than) new drives.

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