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Re: [Xen-users] NFS goes down, XEN hangs

On Mon, Aug 22, 2011 at 8:47 AM, Antonio Pina (antonio.pina)
<antonio.pina@xxxxxxxxxxx> wrote:
> -          2 servers acting as NFS servers hosting Windows and Linux DOMUs
> (Server1 and Server2)

> Everything works very well until we shutdown one of the Servers (Server1,
> for example). As expected, the associated DOMUs stops completely until we
> turn Server1  on again.

> Now, here’s the funny thing: Some of the XEN HOSTS stop working completely!
> A simple “w” command issued in bash hangs until we issue a CONTROL C. The
> only solution is to restart the whole server.

> We still could not found out some pattern. We expected at least the
> Server2’s DOMUs keep running even if the Server1’s DOMUs go offline, but no
> luck.

That's not how nfs works (not by default anyway)

> Has anybody here seen this ? Many thanks !

It's a general issue with nfs (not xen-specific). The default
behaviour of nfs in case of error is "report 'server not responding'
on the console and continue retrying indefinitely" and "not allow file
operations to be interrupted." (see http://linux.die.net/man/5/nfs)

That behaviour can take up enough cpu cycles that you'll be unable to
do anything else (in your example, the "w" command). You MIGHT be able
to work around this by explicitly using "soft" and "intr" mount
option. In that case you will have to manually remount the nfs share
and restart any programs currently using it.


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