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Re: [zfs-discuss] Periodic flush

Subject: Re: [zfs-discuss] Periodic flush
From: Bob Friesenhahn
Date: Thu, 27 Mar 2008 11:24:34 -0500 CDT
On Thu, 27 Mar 2008, Neelakanth Nadgir wrote:
> This causes the sync to happen much faster, but as you say, suboptimal.
> Haven't had the time to go through the bug report, but probably
> CR 6429205 each zpool needs to monitor its throughput
> and throttle heavy writers
> will help.

I hope that this feature is implemented soon, and works well. :-)

I tested with my application outputting to a UFS filesystem on a 
single 15K RPM SAS disk and saw that it writes about 50MB/second and 
without the bursty behavior of ZFS.  When writing to ZFS filesystem on 
a RAID array, zpool I/O stat reports an average (over 10 seconds) 
write rate of 54MB/second.  Given that the throughput is not much 
higher on the RAID array, I assume that the bottleneck is in my 

>> Are the 'zpool iostat' statistics accurate?
> Yes. You could also look at regular iostat
> and correlate it.

Iostat shows that my RAID array disks are loafing with only 9MB/second 
writes to each but with 82 writes/second.

Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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