Date: Fri, 25 May 2012 15:25:09 +1000 From: Jan Mikkelsen <janm@transactionware.com> To: Pete French <petefrench@ingresso.co.uk> Cc: freebsd-stable@freebsd.org Subject: Re: VirtualBox, AIO and zvol's - a cautionary tale Message-ID: <F1C457B5-0CFF-4286-95E0-C9871CA8021A@transactionware.com> In-Reply-To: <E1SXBLw-000AZw-Ee@dilbert.ingresso.co.uk> References: <E1SXBLw-000AZw-Ee@dilbert.ingresso.co.uk>
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Hi, On 23/05/2012, at 11:11 PM, Pete French 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. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > Solution is simple - disable AIO. All then goes back to being nice > and stable again. But it did take a while to find. I have seen similar behaviour, but I did not disable AIO to solve it. = Instead, in the VirtualBox VM, I made sure that the storage controller = was created with the "--hostiocache on" option. Without that, the = virtual machines were unreliable on ZFS with the same behaviour you saw. Do you have the hostiocache enabled or disabled in your VM? Does it make = a difference? Regards, Jan.
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