NFS writes and ZFS

[Bernd Walter]

On Wed, Jul 23, 2008 at 10:24:01AM +0200, Pawel Jakub Dawidek wrote:
> On Tue, Jul 22, 2008 at 11:28:27AM -0400, John Nielsen wrote:
> > I have a FreeBSD server (which I use as a NAS device, among other things) 
> > and a FreeBSD deskop. The desktop is running 7-STABLE from a couple days 
> > ago and the server is running 8-CURRENT from yesterday. The server has 
> > several NFS-exported ZFS'es which I mount from the desktop. Since moving 
> > the shares to ZFS I've been having trouble writing to them from the 
> > desktop--the mount hangs after the first or second attempt. This is 
> > similar if not identical to what's described in the thread 
> > (from -current) I partially copied below.
> > 
> > Today I discovered that the problem seems to go away if I change the NFS 
> > mount options on the desktop. The following is a summary/timeline of what 
> > I've tried:
> > 
> > 7-STABLE client, no NFS options (defaults); 7-STABLE server, UFS; works
> > 7-STABLE client, no NFS options (defaults); 7-STABLE server, ZFS; broken
> > 7-STABLE client, no NFS options (defaults); 8-CURRENT server, ZFS; broken
> > 7-STABLE client, tcp,nfsv3,-r32768,-w32768; 8-CURRENT server, ZFS, works
> 
> Do you need all the options here? If not, could you try to find the
> smallest subset of options that are needed to make ZFS work? Maybe
> 'nfsv3' is all that is needed, or 'tcp' alone fixes it? At work we use
> many NFS exported ZFS file systems, mostly accessed from MacOS X and
> we see no problems.

Whenever changing NFS transport options has an influence on reliability
my first task is to verify the network.
Especially there were often hardware problems with some NIC lately,
of which some have worked around in the drivers and some not.
Disabling TSO and checksum offloading typically helps.
This kind of problem is typical on both the client and server, but also
on routers.
Of course network problems can also be on any cable, switch in between
as well, but are less typical to produce complete NFS hangs.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.