Restarting exports disturbs NFS clients

[Jeremy Chadwick]

On Sat, May 04, 2013 at 03:08:43PM -0400, Daniel Feenberg wrote:
> 
> When we change the exportfs file on our FreeBSD 9.1 fileserver and signal
> mountd to reread the file:
> 
>    kill -HUP `cat /var/run/mountd.pid`
> 
> it kills the jobs on  clients that have files open on the fileserver. They
> terminate with an I/O error. The same thing happens if NFS is restarted.
> 
> This is pretty inconvenient for users (and us). Is there a way
> around this? We have noticed that a Linux fileserver can restart nfs
> without distrubing clients (other than a short pause). The Linux
> restart doesn't restart the locking mechanism - is that the
> difference? We could do without locks, even without NFSv4, for that
> matter, if it would let us change exports without disturbing users.
> Perhaps there is an NFS shutdown procedure that we should be using?

http://svnweb.freebsd.org/base/stable/9/usr.sbin/mountd/mountd.c?view=log

See commit r243739.

TL;DR -- Try running stable/9 instead of 9.1-RELEASE.

-- 
| Jeremy Chadwick                                   jdc at koitsu.org |
| UNIX Systems Administrator                http://jdc.koitsu.org/ |
| Mountain View, CA, US                                            |
| Making life hard for others since 1977.             PGP 4BD6C0CB |