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

["Antonio Pina (antonio.pina)" <antonio.pina@xxxxxxxxxxx>]

Thank you for your answer.

I understand and agree with your point but it's not the case. As soon as 
Server1 comes back, the NFS directory becomes available again (ls -l /server1 
works). The CPU is low as usual and I can use some commands like "xl list", but 
now other commands, like "w" I said before.

Thank you.


-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Fajar A. Nugraha
Sent: Sunday, August 21, 2011 11:12 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: 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.

--
Fajar

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