NFS writes and ZFS

[John Nielsen]

On Wednesday 23 July 2008, 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.

No. "tcp" alone fixes it. That's not too surprising since nfsv3 should be a 
no-op. With everything _but_ "tcp" it took only slightly longer to hang the 
mount (not scientifically measured).

With the default NFS mount mode changed to TCP in -CURRENT the workaround is 
already in place for FreeBSD clients, and the issue apparently never popped 
up on other clients--there are a few people (yourself included) who say 
they've never had a problem with Mac OS, e.g.. I haven't come across 
reports either way about Solaris or Linux. Are we the last ones to use UDP 
by default?

Anyway, I hope this is helpful. Let me know if I should file a PR or 
anything.

Thanks,

JN