Re: [Xen-users] Xen reboots on dom-U disk stress...

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Yes, spot on, it was running out of page space in dom-0 after which
> Linux seemed to go on a process killing spree before turning the gun on
> itself and rebooting. Not very pretty.

Yuk.  Computer guts ;-)

> And yes, NFS + loopback looks particularly ugly. I got it to finally run
> with 1G in dom-0!

Yowee!  I've looked in portions of both the NFS and the loopback code but I 
admit I don't really know why it's such a memory hog :-/

> We're trying GNDB, iSCSI et al... (any preferences?)

From what I've heard, GNBD works pretty well and has the best performance of 
the NBDs.  iSCSI is more sophisticated but may well be overkill for your 
needs.

With GNBD I imagine it's a simple matter to get the daemon to serve out the 
disk file, so it should be pretty easy to convert your setup.  You could then 
either have the domain use GNBD root (probably booting with an initrd), or 
just re-export the device from dom0 as you have been doing.

Cheers,
Mark

> Thanks
> Roland
>
> Mark Williamson wrote:
> >How much memory does dom0 have?  I believe NFS + loopback files is very
> > prone to out-of-memory problems so it seems most likely your dom0 died.
> >
> >If you hook up a serial line, you might be able to get some useful output
> >before it dies.
> >
> >Had you considered using something like GNBD instead of NFS + loopback? 
> > It should perform better and be less prone to OOM problems.
> >
> >Cheers,
> >Mark
> >
> >On Wednesday 11 May 2005 08:36, Roland Paterson-Jones wrote:
> >>Hi all
> >>
> >>I tried to run bonnie++ disk stresser in dom-U, who's disk is backed
> >>with non-local (on nfs) loop-back file.
> >>
> >>The machine rebooted pretty quickly.
> >>
> >>So, how do I tell what's barfing? Is it Xen? Is it dom-0 (nfs or
> >>loop-back)?
> >>
> >>I looked in dom-0's /var/log/messages and didn't see any obvious record
> >>of a dom-0 whoopsie (but is that the right place to look etc...).
> >>
> >>Any help greatfully received.
> >>
> >>Incidently, I ran bonnie++ successfully in dom-U with disk backed by
> >>local (dom-0 ext3) loop-back file. This pleasantly surprised me, as
> >>loop-back files don't have a good rep for stability under load.
> >>
> >>Regards
> >>Roland
> >>
> >>
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