Comment 10 for bug 494476

As suggested by Brian Rogers in bug #276476 I'm posting an update here. Hope to attract some attention!

I'm running a file server that shares home directories and other directories (~4TB, ext4) to 4 linux clients via nfs and about 20 windows and mac clients via samba. Rsync runs several times per day to mirror all files onto a second server. This seems to be the main trigger for the freezes to happen but I've seen it being caused by other I/O intensive operations, too.
Mostly, the file server recovers 'quickly' and the freezes only last for 10 to 60 seconds. Such interruptions occur at least once per hour.
When working on a linux client, everything stops (possibly due to the shared ~) until the file server has recovered. On windows clients the program accessing the share freezes. During that time, the load of the server increases rapidly as more and more processes are queuing up for a read/write.
Rebooting the server helps but the first 120 second block normally happens within several hours and rebooting every time is not an option.
Blocked tasks include pdflush, nfsd and kjournald2.
OS is Ubuntu karmic 9.10 on 2.6.31-21-server #59-Ubuntu SMP Wed Mar 24 08:26:06 UTC 2010 x86_64
All packages updated