Hi all, I am working on a project in which I would like to use copy-on-write VM disk images in order to create "deltas" of a disk over a period of time. For example, if I have a VM which uses /var/lib/xen/vm1/vm1.hda as its disk image, can I attach a copy-on-write disk image which would record changes in, /var/lib/xen/vm1/vm1-cow.hda rather than in the main disk image file? I''ve seen some of the projects listed on http://wiki.xensource.com/xenwiki/COWHowTo but am not sure if something like this is actually possible. If anyone has ever configured something like this, I''d be interested in any notes or opinions you can provide about this kind of configuration, or possibilities for entirely different setups which do the same thing. Thanks, Eric _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Eric Harney wrote:> If anyone has ever configured something like this, I''d be interested in any > notes or opinions you can provide about this kind of configuration, or > possibilities for entirely different setups which do the same thing. >I haven''t done it personally, but you could try using LVM''s snapshot feature to create one or several disk images based on a single original image whose changes would be stored in the snapshot storage. You''d want to make sure you had enough room for the storage of all changes of course. -- Michael T. Babcock http://mikebabcock.ca _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
There''s support for an virtual disk type (I think it''s tap:qcow) in the blocktap driver which allows you to use QEmu''s QCow format to store deltas. Support for this has certainly been in -unstable, I don''t recall if it made it into 3.1. You can''t switch a disk to be COW "on the fly" so you''d need to configure it like that on boot. I''m not sure how much you''re able to control the COW process under Xen (i.e. starting a new COW file, layering delta files etc).> > I''ve seen some of the projects listed on > http://wiki.xensource.com/xenwiki/COWHowTo but am not sure if something > like this is actually possible.There are various DM and LVM snapshot techniques which can also do various kinds of snaphots. Cheers, Mark -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
"Michael T. Babcock" <mike@mikebabcock.ca> writes:> Eric Harney wrote: >> If anyone has ever configured something like this, I''d be interested in any >> notes or opinions you can provide about this kind of configuration, or >> possibilities for entirely different setups which do the same thing. >> > > I haven''t done it personally, but you could try using LVM''s snapshot > feature to create one or several disk images based on a single > original image whose changes would be stored in the snapshot storage. > You''d want to make sure you had enough room for the storage of all > changes of course. > > -- > Michael T. Babcock > http://mikebabcock.caAlternatively (and if speed is not so important) you can use fuse-unionfs with nfs shares (and nfs is slow, not fuse). I have the following setup: /mnt/disk is exported read-write /mnt/group/<group> is read-write /mnt/client/<ip> is read-write On disk I have a generic debian that is shared between all clients. group/<group> contains changes relevant for all clients in a group (like group lustre, debug, etc) and last client/<ip> is where every client writes all their changes to. The advantage of fuse-unionfs over other union FS implementations is that you can savely edit files on /mnt/disk or /mnt/group without causing oopses on the client or plain wrong data being cached. MfG Goswin _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users