immense delayed write to file system (ZFS and UFS2), performance issues

[Morgan Wesström]

O. Hartmann wrote:
> 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


The disks involved don't happen to be Western Digital Green Power disks,
do they? The Intelli-Park function in these disks are wrecking havoc
with I/O in Linux-land at least, causing massive stalls and iowait
through the roof during the 25-30 seconds it takes for the heads to
unload after parking. I have two of these disks sitting on my desk now
collecting dust...
/Morgan