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I am looking to set up a new server. I can only use Intel 520 Series 240gb MLC ssds or standard Seagate 7200rpm disks.
These are the non negotiable options.

Naturally, as this is going to be running MySQL with its primary task being a MySQL server. As the biggest performance bottleneck being disk I/O, I would prefer to use the SSDs.

I need to have close to 1TB of disk space. Now, RAID5 does not give the best performance and is rumoured to not be best for SSDs, so I am looking at a Raid 10(1+0) setup which would give me 720gb (240gb * 3)

I need to know how I can set this up with Ubuntu 12.04.01 LTS using software raid and to make sure that TRIM support (Discard I think its called in Linux) is enabled for the raid config.

Has anyone don't this successfully? Any howto info and stuff to watch out for and basically what tools to use and so on would be of great assistance.

Ideally, I also need to be able to boot off the SSD raid array.

Can anyone point me in the right direction ?


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1 Answer 1

The answer is "it depends" and you should really understand what TRIM does before asserting such an inflexible position.


MD RAID needs specific support to forward DISCARD requests and that hasn't even been proposed until 3.6, therefore the support will not be in the precise kernel. I just looked, it's not there.


SSDs are nice and all, but they are most cost effective when combined with high RPM magnetic storage. For example, use a RAID 1 SSD array to house the filesystem journal while the filesystem is backed by a RAID 10 consisting of 15K disks.


The higher the RPMS, the lower your worst seek time is, random IO loads benefit the most from high RPM backing stores. SQL can be write intensive, so any parity calculation is a bad idea e.g. RAID 4 and 5.

The organization of the RAID and the filesystem is just as important as the backing store.

You can always TRIM your disks manually, weekly is fine to start, you should observe what the performance impact is before running it more frequently. Oh, they will burn out so it would be a good idea to estimate how many write/delete cycles your SSDs have and service the RAID 1 one leg at a time.


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