From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Writing a tool for Shared Persistent Windows Boot Image Date: Thu, 21 Jun 2007 13:11:28 -0500 Message-ID: <467ABF50.50209@codemonkey.ws> References: <2BB087BE-D323-4D8E-82F7-794C76ED2BCD@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <2BB087BE-D323-4D8E-82F7-794C76ED2BCD@gmail.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jim Burnes Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Jim Burnes wrote: > Before, in my "Hard Problem" email I was trying to communicate a design > issue were trying to solve with Xen. > > This is what we need to do: > > 1) Deploy 24 Windows XP VMs in parallel. I have strong doubts that this would be kosher from a licensing perspective, however... > 2) Boot them from a shared Windows XP C: drive. > 3) Since this is a read-only shared image we obviously can't have > multiple VM's writing to it. > 4) All writes to the boot image for logging, registry and other purposes > should be diverted to an auxiliary shadow drive specific to each VM. If you start with a single image, and then create "COW" files using the qcow format, then you can have a shared base image. > 5) After we shut down the VM we need to mount and examine the contents > of the shadow drive Mounting is tricky. If you look on qemu-devel, you'll find a couple references to tool that allow you to mount a qcow file (usually with nbd). > 6) When we are done examining the contents of the shadow drive, we need > to fast format it for the next VM to use. You can just delete the cow file and create a new one. Regards, Anthony Liguori > Is this supported natively in Xen? What does everyone else who needs to > run a lot of Windows VMs do? There must be a way to support shared images. > > The reason I posted this to xen-devel is that I could probably implement > a UnionFS for Windows by writing a kernel hook and intercepting all > reads and writes to the C: drive, but I don't have enough time to do > that right now. Because of schedule constraints, if we don't find a way > to do this in Xen/XenSource we'll have to drop Xen and move on to VMWare > ESX at considerable cost to our project. > > Are there any senior Xen software engineers out there who've done this > or who might know how? > > Thanks, > > Jim Burnes