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

From: Ogden <lists(at)darkstatic(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
Date: 2011-08-18 03:48:09
Message-ID: 207E881B-73CD-4C31-A863-2C238838C41F@darkstatic.com (view raw or flat)
Thread:
Lists: pgsql-performance
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 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.


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 good enough 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, what is usually a good filesystem to use? I keep reading conflicting things..

Thank you

Ogden



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