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Re: df hangs -- nfs related problem



Craig White wrote:
On Wed, 2009-01-07 at 10:31 -0800, Aldo Foot wrote:
On Wed, Jan 7, 2009 at 7:16 AM, Patrick O'Callaghan
<pocallaghan gmail com> wrote:
On Wed, Jan 7, 2009 at 9:33 PM, Rick Stevens <ricks nerd com> wrote:
Try "lsof | grep nfs" to see if anything has the mountpoint open.  If
not, try "umount -f /mnt/nfs" as the root user to try a forced umount.

Also check to see if the mount command (or /etc/fstab entry) has "hard"
specified (that's the default as well).  Unless you're really certain
about the stability of the network and of the NFS server, I'd recommend
you specify "soft" in the mount command (see "man 5 nfs" for details).
That would depend on which is worse, potentially losing data or having
a client machine hang because the server is (perhaps temporarily)
unavailable. It depends totally on the specific application scenario.
To quote nfs(5):

<quote>
A  so-called  "soft"  timeout can cause silent data corruption in
certain cases. As such, use the soft option only when client
responsiveness is more important than data integrity.  Using NFS over
TCP or increasing the value of the retrans option  may  mitigate some
of the risks of using the soft option.
</quote>

IOW there is no "right" answer to this.

poc
The command "umount -f" fixed my problem. Thanks Rick.

You're welcome.

I had tried "umount -k", which works in older RedHat8
boxes; clearly I've got to re-read the man pages now and then.

It's caught me, too.


So, it appears a soft mount may be ok for read-only operations but not
ideal for things such as remote X-applicatons or filesystems
such as /home or /var/mail. It's wise to make the distinction between hard
and soft mount --great pointer.
----
I have switched over to mostly using automounts which connect/disconnect
when needed and I have been using

-rsize=8192,wsize=8192,intr

as a basic setup. Obviously I could tune the rsize/wsize and perhaps
figure out that a larger number would give me better performance but I
found that the intr option seemed to provide the soft landing when
needed. These are the users home directories and function for a number
of connections/users/systems without any fuss.

Yeah, "intr" is nice.  Forgot about that one.
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