Re: Problem with nfs server reboot causing exports to jumble

[wsnyder-12vJDDTx9R9AfugRpC6u6w@public.gmane.org (Wilson Snyder)]

>Wilson,
>
>On Thu, Feb 25, 2010 at 02:29:10PM -0500, Wilson Snyder wrote:
>> 
>> We're using the 2.6.18 x86_64 kernel (RH SL 5.1) with a NFS
>> v3 server and NFS v3 clients using the automounter with options
>> (rw,noatime,hard,intr,rsize=32768,wsize=32768,proto=tcp).
>> 
>> Our NFS server had several exports
>> 
>>     /export/a/{files-a}
>>     /export/b/{files-b}
>> 
>> these were mounted on various clients.
>> 
>> We then added a new mount and export without rebooting:
>> 
>>     /export/a/{files-a}
>>     /export/b/{files-b}
>>     /export/c/{files-c}
>> 
>> All were visible on the clients, and everything was fine:
>> 
>>     /nfs/a/{files-a}
>>     /nfs/b/{files-b}
>>     /nfs/c/{files-c}
>> 
>> Our NFS server then crashed, and rebooted.  After reboot the
>> clients then had:
>> 
>>     /nfs/a/{files-c}
>>     /nfs/b/{files-a}
>>     /nfs/c/{files-b}
>> 
>> Note the files correspond to the wrong exports.  Remounting
>> on every client fixed the problem - once we realized what
>> was going on!  (files-a/b/c were all similar so it wasn't
>> immediately aparent)
>> 
>> My speculation is the reboot changed some enumeration
>> causing a mismatch between the clients and servers.
>> 
>> This is a new one by me - is this a known issue, and if so
>> is a patch available?
>> 
>> Other than patching, are there any precautions we can take
>> to avoid this in the future?  (Other than not crashing the
>> server, which we'd be happy to not to do. :)
>
>Use the mp and fsid export options documented in the exports manpage.

Reading between the lines, are you suggesting the mounts
weren't ready when the exports started (or from the
pre-reboot's mount), causing the fsid's to be identical?  I
could see that happening.

I presume then that it's enough to just use mp - assuming
each mountpoint has a unique UUID?  Wouldn't adding fsid now
(with the server and clients all up) require me to remount
every client?

Finally, is there a way to examine the present
(automatically assigned) fsid's so I can confirm this was
the problem?

Thanks much