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Date: Tue, 31 Aug 2010 15:21:59 +0200
From: Giulio Ferro <auryn@zirakzigil.org>
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Subject: About zfs + nfs stability
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I have a 8.0 stable (last build around April 2010) which I use as a nfs
server : amd64, 8GB RAM, ~7TB storage.

I had a lot of grief with the (sadly) well know "kmem map too small" 
bug, which really compromised the quality of the service that server
was deputed to.

There wasn't (and there still isn't) any relevant indication in the
official freebsd zfs documentation on how to bypass the problem.
Only thanks to the effort and goodwill of other users in this list
and with hours on end of trying,
I could come up with something working:
(in /boot/loader.conf)
vm.kmem_size="6096M"
vfs.zfs.arc_max="3584M"
vfs.zfs.prefetch_disable="1"
vfs.zfs.txg.timeout="5"

The freezes are gone, thankfully, but I often get huge slow-downs: 
looking in the logs of the nfs clients I get plenty of:
... kernel: nfs server ...:/path/to/dir: lockd not responding
... kernel: nfs server ...:/path/to/dir: lockd is alive again

I don't know if this has anything to do with zfs.
What I'd like to know is the answer to the following questions
by other users and/or developers.

I don't need opinions, only punctual facts people have verified for
themselves.

1) Is it a good idea to upgrade this production system to the latest 8 
stable (8.1 stable I believe)? Is it really stable?
2) Are the zfs aforementioned tuning in /boot/loader.conf still necessary?
3) Is it a good idea to switch to nfsv4? Performance? Stability?

and above all:

4) will I get a more stable and performant system by upgrading?

Thanks in advance for the answers...