df hangs -- nfs related problem

[Rick Stevens]

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 at gmail.com> wrote:
>>> On Wed, Jan 7, 2009 at 9:33 PM, Rick Stevens <ricks at 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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- Rick Stevens, Systems Engineer                      ricks at nerd.com -
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