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

On Aug 17, 2011, at 4:17 PM, Greg Smith wrote:

> 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.

I have mounted the ext4 system with the nobarrier option:

/dev/sdb1 on /var/lib/pgsql type ext4 (rw,noatime,data=writeback,barrier=0,nobh,errors=remount-ro)

Yet the results show absolutely a decrease in performance in the ext4 "Sequential Output - Block" results:

http://malekkoheavyindustry.com/benchmark.html

However, the Random seeks is better, even more so than XFS...

Any thoughts as to why this is occurring?

Ogden