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

[Aragon Gouveia]

On 01/18/10 22:13, O. Hartmann wrote:
> 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.

I'm experiencing the same thing, except in my case it's most noticeable 
when writing to a USB flash drive with a FAT32 filesystem.  It slows the 
entire system down, even if the data being written is coming from cache 
or a memory file system.

I don't know if it's related.  I'm running 8-STABLE from about 4 December.


Regards,
Aragon