VirtualBox, AIO and zvol's - a cautionary tale

[Adrian Chadd]

Hi,

Can you please file a PR? Having broken AIO and ZFS would be .. bad.



adrian


On 23 May 2012 06:11, Pete French <petefrench at ingresso.co.uk> wrote:
> Am posting this to stable not really as a question, but more in case anyone
> else hits the same problem. Last patch tuesday one of my virtual Windows
> machines  running under VirtualBox started crashing. By which I mean
> that VirtualBox would quit. This had been running tsably for a long
> tine, so it puzzled me.
>
> First thought was it was sme patch from patch-tuesday. But rolling back
> to an earlier version of the disc showed it wasn't - the crashes were
> occurring before the patch had been applied.
>
> I'll skip the hours of puzzlement which followed - it turrned out that
> the indirect cause was that a few weeks ago I had installed Samba
> onto the same server. In doing so I had enabled AIO, as this improves
> Samba performance.
>
> What I didn't realise is that if VirtualBox finds AIO loaded it proceeds
> to use it.  So by doing that I had switched on AIO inside my virtual
> machines as well. The disc I use for my virtual machines are all zvols (it
> performs better, and it seems that VirtualBox has a problem using AIO
> to access zvols.
>
> But this didn;t show up for weeks because in the normal scheme of things
> my virtual machines dont acccess the local dirve very much. It was only
> when they started downloading patches that the crash happened.
>
> Solution is simple - disable AIO. All then goes back to being nice
> and stable again. But it did take a while to find.
>
> Hope someone else finds the info usefull!
>
> -pete.
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