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

On Aug 17, 2011, at 4:16 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
configuredwith RAID 10. The drives are the same (SAS 15K). I tried the new system with ext3 and then XFS but the
resultsseem 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
onyour 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
andthe XFS results, not far lower than either.  Normally this only comes from using a bad set of mount options.  With a
battery-backedwrite cache, you'd want to use "nobarrier" for example; if you didn't do that, that can crush output
rates.


Isn't this very dangerous? I have the Dell PERC H700 card - I see that it has 512Mb Cache. Is this the same thing and
goodenough to switch to nobarrier? Just worried if a sudden power shut down, then data can be lost on this option.  

I did not do that with XFS and it did quite well - I know it's up to my app and more testing, but in your experience,
whatis usually a good filesystem to use? I keep reading conflicting things.. 

Thank you

Ogden