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Are there any notable differences, other than (awesome) performance, when running RAID arrays made up of solid state drives? I'm considering one of the two:

  • 4 x 256GB SSD in RAID-10 (total usable array size = 512GB).
  • 6 x 256GB SSD in RAID-50 (total usable array size = 1024GB).

Are there any differences, from a end-user/setup point-of-view, in using SSDs in RAID arrays as opposed to regular HDDs?

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3 Answers 3

up vote 2 down vote accepted

you won't get TRIM support today, but Intel announced that they will support it with the upcoming versions of their drivers as of version 11.5. (Only for RAID 0, though)

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I assume this is just for high availability (the raid-1 portion), and greater storage volume per logical disk (raid-0).

If that is the intent, sure why not?

Performance-wise, you probably will not see significant improvement. The big wins of RAID were due mostly to combating rotational latency. SSD completely squashes that, so the performance gains should be negligible. I suppose you might get throughput gains, assuming you really need to push 500MByte/sec+

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The goal is to get parity (hence RAID-5 or 1) without any degraded performance, with hopefully better performance than stock, hence RAID-0. Thoughts? Does using RAID-0 actually help performance at all in SSDs? –  Naftuli Tzvi Kay Jan 9 '12 at 21:08
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RAID-5 should be marked out.. It has poor write performance characteristics, and the degraded mode performance is usually quite poor until the rebuild completes (assuming you had a hotspare). If looking for parity alone, RAID-1 is pretty effective. Or consider a filesystem like ZFS for checksums (which is ultimately what you are after). –  spydum Jan 9 '12 at 22:36
    
RAID 1 is a straight mirror, there is no parity data in RAID 1. I think you are confusing just redundancy with parity. Raid levels 2 through 5 have parity data to create different kinds of redundancy. –  Paperlantern Jan 10 '12 at 3:26

You would loose TRIM, which, depending on what you are doing, might matter, or it might not.

Traditionally RAID was about spreading out the IO requests to mask latency and while the latency of SSDs is a lot lower they can still benefit from this. But that does require a RAID solution that adds very little latency. I suspect most RAID cards will add more latency than you gain by this and thus end up hurting performance.

RAIDing SSD does scale the throughput very well. RAID-0 of two SSD effectively doubled the throughput. So anything that is limited by throughput would greatly improve from RAIDed SSDs.

As for RAID-10 vs RAID-50 I would go with 10, simply because I suspect that even a really beefy RAID card would end up a bad bottleneck due to the parity calculations, especially in smaller writes.

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