RAID-5 and database servers

Matt Domsch Matt_Domsch at dell.com
Tue Mar 9 17:12:09 CST 2010


On Tue, Mar 09, 2010 at 04:54:44PM -0600, John G. Heim wrote:
> Has anyone configured a database server with RAID-5? Is it really a bad idea 
> to do so? I asked last month for tips on configuring a DB server. I have 
> around $6K to spend. I am pretty much settled on getting 2 quad-core CPUs 
> and 32 Gb of RAM. But I'm still ignorant in terms of what to get for disk. 
> 1500 RPM, I know that. But is it better to do RAID-1 or RAID-5. I can't 
> figure out why RAID-1 would be better than RAID-5. I understand that with 
> RAID-5, a single database write might translate into writing 2 blocks (a 
> data block and a parity block). But doesn't RAID-1 *always* do an extra 
> write for every data block written?

RAID 5's problem isn't the extra write.  It's that to write a hunk
that's not a whole stripe width (64k * (num_drives - 1)) it has to
first read a whole stripe (num_drives-1), calculate the parity, and
then write to 2 disks.

-- 
Matt Domsch
Technology Strategist, Dell Office of the CTO
linux.dell.com & www.dell.com/linux



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