[ale] Building a Linux/Mysql Database server.

[The Don Lachlan]

On Tue, May 24, 2011 at 07:37:16AM -0400, LinuxGnome wrote:
> I would go with many 15k drives for the data (for example, if you have a 500G DB, then 9x 73G drives in RAID5 will you 6~8 times the performance of one 600G drive that is IO bound).  You might consider a ramdrive (i.e. FlashCache, not SDD) for writing your logs to.

Do NOT use RAID5. Ever. For ANYTHING. Unless you're trying to show exactly
how much it sucks in comparison to RAID10.

http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt
http://www.zdnet.com/blog/storage/why-raid-5-stops-working-in-2009/162

If you are absolutely wedded to parity, use RAID6. But really, you should
still use RAID10.

http://storagemojo.com/2010/02/27/does-raid-6-stops-working-in-2019/

The math is already out there. In RAID5, you can only survive one disk
failure - two concurrent disk failures and you're dead. RAID10 may fail
after two concurrent disks failures but it can survive up to n/2 disk
failures, depending which disks fail, and the odds are higher that drives in
different mirrors will fail rather than in the same mirror.

Then, you want to rebuild. In RAID5, you have to read from n-1 disks to
rebuild, whereas RAID10 requires you to read 1 disk. As disks increase in
size, the probability of a read error during a rebuild approaches 100%,
which is more likely under RAID5 than RAID10 because you're reading more
disks and more data. Read error == failed rebuild. Some current drives are
large enough that it is a certainty in a RAID5 rebuild.

Do. NOT. Use. RAID5.

-L