From: | Scott Carey <scott(at)richrelevance(dot)com> |
---|---|
To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Kenneth Cox <kenstir(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Advice configuring ServeRAID 8k for performance |
Date: | 2010-08-16 16:28:52 |
Message-ID: | 5687A8AD-CA70-4272-A32C-6AE5F491CEA4@richrelevance.com |
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Thread: | |
Lists: | pgsql-performance |
Don't ever have WAL and data on the same OS volume as ext3.
If data=writeback, performance will be fine, data integrity will be ok for WAL, but data integrity will not be sufficient for the data partition.
If data=ordered, performance will be very bad, but data integrity will be OK.
This is because an fsync on ext3 flushes _all dirty pages in the file system_ to disk, not just those for the file being fsync'd.
One partition for WAL, one for data. If using ext3 this is essentially a performance requirement no matter how your array is set up underneath.
On Aug 13, 2010, at 11:41 AM, Greg Smith wrote:
> Bruce Momjian wrote:
>> We recomment 'data=writeback' for ext3 in our docs
>>
>
> Only for the WAL though, which is fine, and I think spelled out clearly
> enough in the doc section you quoted. Ken's system has one big RAID
> volume, which means he'd be mounting the data files with 'writeback'
> too; that's the thing to avoid.
>
> --
> Greg Smith 2ndQuadrant US Baltimore, MD
> PostgreSQL Training, Services and Support
> greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us
>
>
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