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 15:39:59 -0500 Message-ID: <467AE21F.1020700@codemonkey.ws> References: <2BB087BE-D323-4D8E-82F7-794C76ED2BCD@gmail.com> <467ABF50.50209@codemonkey.ws> <13A934B9-F615-4838-8D26-4E33F0BCFF2E@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: <13A934B9-F615-4838-8D26-4E33F0BCFF2E@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 , Xen Mailing List List-Id: xen-devel@lists.xenproject.org Jim Burnes wrote: >> If you start with a single image, and then create "COW" files using >> the qcow format, then you can have a shared base image. >> > > Let me make sure I understand your answer. COW files are sparse > storage for the QEMU environment (which tools you use for Xen). > > We want a static filesystem image that represents a snapshot of a > Windows XP system right after boot. When we activate that image we > want to perform a few housekeeping issues (like set the MAC and > re-DHCP etc), but we also want to make sure that any writes to the > image are redirected to an overlay writable file system. In other > words we want a single shared image of the OS itself with all writes > going to the COW / shadow image of that specific VM. COW == Copy On Write. It's a separate file that only stores the data that has been written since the cow was created. > Is the COW file you speak of overlayed on top of a single static > Windows image or does the COW file contain the entire Windows XP boot > image plus any writes. It just contains the writes after the COW was created. > I know this depends on your previous answer, but if we delete the COW > doesn't that delete the XP boot image also? If you delete the COW, the underlying base image is unaffected. > If the COW file is used as an extent-space to the static Windows XP > image, then that should work. > > Otherwise I think it would require a recreation of the full Windows XP > image. Ideally that image can be kept static as the continual > deletion and re-creation of relatively large COW files would be > time-consuming and would tend to fragment hard disk space. You really shouldn't worry about disk fragmentation but that's a whole other thread :-) Regards, Anthony Liguori > Other than that, I'm very grateful for your kind assistance. > > Thanks again, > > Jim Burnes > Boulder, CO > >