Re: Filesystem benchmarking for pg 8.3.3 server

On Aug 11, 2008, at 9:01 AM, Jeff wrote:
> On Aug 11, 2008, at 5:17 AM, Henrik wrote:
>
>> OK, changed the SAS RAID 10 to RAID 5 and now my random writes are
>> handing 112 MB/ sek. So it is almsot twice as fast as the RAID10
>> with the same disks. Any ideas why?
>>
>> Is the iozone tests faulty?
>
>
> does IOzone disable the os caches?
> If not you need to use a size of 2xRAM for true results.
>
> regardless - the test only took 10 seconds of wall time - which
> isn't very long at all. You'd probably want to run it longer anyway.

Additionally, you need to be careful of what size writes you're
using. If you're doing random writes that perfectly align with the
raid stripe size, you'll see virtually no RAID5 overhead, and you'll
get the performance of N-1 drives, as opposed to RAID10 giving you N/2.
--
Decibel!, aka Jim C. Nasby, Database Architect decibel(at)decibel(dot)org
Give your computer some brain candy! www.distributed.net Team #1828