Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++

On 08/17/2011 02:26 PM, Ogden wrote:
> I am using bonnie++ to benchmark our current Postgres system (on RAID
> 5) with the new one we have, which I have configured with RAID 10. The
> drives are the same (SAS 15K). I tried the new system with ext3 and
> then XFS but the results seem really outrageous as compared to the
> current system, or am I reading things wrong?
>
> The benchmark results are here:
> http://malekkoheavyindustry.com/benchmark.html

Congratulations--you're now qualified to be a member of the "RAID5
sucks" club.  You can find other members at
http://www.miracleas.com/BAARF/BAARF2.html  Reasonable read speeds and
just terrible write ones are expected if that's on your old hardware.
Your new results are what I would expect from the hardware you've
described.

The only thing that looks weird are your ext4 "Sequential Output -
Block" results.  They should be between the ext3 and the XFS results,
not far lower than either.  Normally this only comes from using a bad
set of mount options.  With a battery-backed write cache, you'd want to
use "nobarrier" for example; if you didn't do that, that can crush
output rates.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us