From owner-freebsd-stable@FreeBSD.ORG Wed May 23 13:11:50 2012 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2F6B8106564A for ; Wed, 23 May 2012 13:11:50 +0000 (UTC) (envelope-from petefrench@ingresso.co.uk) Received: from constantine.ingresso.co.uk (constantine.ingresso.co.uk [IPv6:2a02:b90:3002:e550::3]) by mx1.freebsd.org (Postfix) with ESMTP id C36348FC19 for ; Wed, 23 May 2012 13:11:49 +0000 (UTC) Received: from dilbert.london-internal.ingresso.co.uk ([10.64.50.6] helo=dilbert.ingresso.co.uk) by constantine.ingresso.co.uk with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76 (FreeBSD)) (envelope-from ) id 1SXBLw-000Fgt-FK for freebsd-stable@freebsd.org; Wed, 23 May 2012 14:11:48 +0100 Received: from petefrench by dilbert.ingresso.co.uk with local (Exim 4.77 (FreeBSD)) (envelope-from ) id 1SXBLw-000AZw-Ee for freebsd-stable@freebsd.org; Wed, 23 May 2012 14:11:48 +0100 To: freebsd-stable@freebsd.org Message-Id: From: Pete French Date: Wed, 23 May 2012 14:11:48 +0100 Subject: VirtualBox, AIO and zvol's - a cautionary tale X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 May 2012 13:11:50 -0000 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.