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Date:      Mon, 18 Jan 2010 21:13:52 +0100
From:      "O. Hartmann" <ohartman@mail.zedat.fu-berlin.de>
To:        FreeBSD Stable <freebsd-stable@freebsd.org>, freebsd-questions@freebsd.org
Subject:   immense delayed write to file system (ZFS and UFS2), performance issues
Message-ID:  <4B54C100.9080906@mail.zedat.fu-berlin.de>

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I realise a strange behaviour of several FreeBSD 8.0-STABLE/amd64 boxes. 
All boxes have the most recent STABLE. One box is a UP system, two 
others SMP boxes, one with a Q6600 4-core, another XEON with 2x 4-cores 
(Dell Poweredge III).

Symptome: All boxes have ZFS and UFS2 filesystems. Since two weeks or 
so, sometimes the I/O performance drops massively when doing 'svn 
update', 'make world' or even 'make kernel'. It doesn't matter what 
memory and how many cpu the box has, it get stuck for several seconds 
and freezing. On the UP box, this is sometimes for 10 - 20 seconds.
A very interesting phenomenon is the massively delayed file writing on 
ZFS filesystems I realise. Editing a file in 'vi' running on one XTerm 
and having in another Xterminal my shell for compiling this file, it 
takes sometimes up to 20 seconds to get the file updated after it has 
been written. It's like having an old, slow NFS connection with long 
cache delays.
These massively delayed file transactions are not necessarely under 
heavy load, sometimes they occur in a relaxed situation. They seem to 
occur much more often on the UP box than on the SMP boxes, but this 
strange phenomenon also occur on the Dell Poweredge II, which has 16GB 
RAM and summa summarum 16 cores. This phenomenon does occur on ZFS- and 
UFS2 filesystems as well. It is hardly reproducable.

Is there any known issue?

Ragrds,
Oliver



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