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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: (view raw or whole 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:
> Congratulations--you're now qualified to be a member of the "RAID5 sucks" club.  You can find other members at  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


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