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I'm considering moving a large database from mechanical disks to SSDs. My initial instinct was to go for RAID 10, but further research suggests that this configuration can significantly reduce the random access performance of the SSDs.

The database is very much read heavy and it's generally generating large data reports, so my assumption is that there is very little by way of sequential workload.

The main alternative suggested to RAID 10 when it comes to SSDs is RAID 1. Of course, this limits me to the size of a singe disk which is, realistically, going to be less than 1TB. This is not ideal.

I guess my question is, just how significant is the random access hit and, assuming I need greater capacity than a single drive can offer, what is a good alternative? Bear in mind this is a Server 2008 box so fancy ZFS solutions or the like are, sadly, not an option.

womble
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Sufo
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2 Answers2

9

Whoever told you that RAID 10 is somehow inherently slower than RAID 1 doesn't know what they're talking about. That makes the rest of the question unanswerable as it's based on a false assumption.

Further reading: What are the different widely used RAID levels and when should I consider them?

Community
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Chris S
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You may have misunderstood someone. RAID-5 is slower than RAID-10 on writes, but RAID-1 can be treated as a RAID-10 with a single pair of disks, and thus has the same performance per "spindle" as RAID-10.

The best recommendation for SSD on a database is to use RAID-5. The rebuild time on the incredibly small and fast SSD drives is very good. Since you'll be doing mostly reads, the only penalty for using a RAID-5 (write overhead due to parity calculations) is not going to affect you greatly. The advantage is that you get to take advantage of SSD performance on a larger slice of your capacity. Going to RAID-10 (or RAID-1) will have a space penalty of 50%.

Of course, you need to make sure you have a hot spare SSD ready to spare in as soon as a disk fails, regardless of whether you use RAID-10 or RAID-5.

Basil
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