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Date: Sat, 26 Sep 2009 09:48:38 +1000
From: Andrew Snow <andrew@modulus.org>
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To: Scott Ullrich <sullrich@gmail.com>
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Cc: freebsd-fs@freebsd.org
Subject: Re: Slow disk write IO with ZFS / NFS
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Scott Ullrich wrote:
> Does anyone have any pointers on how to speed this up without putting
> the data in jeopardy during a power failure, etc (ie: leaving ZIL on).

NFS writes are syncronous so ZFS is constantly syncing small datablocks 
to disk.  By default the transaction log is stored on the same disks as 
the rest of the data.

You might like to try an async NFS mount, but this isn't much different 
from just turning off the ZIL.

Failing that, Add a log device to the pool, SSD or ramdisk is ideal, but 
separate disk HDD spindles to your data zpool also works pretty well.


- Andrew