From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikola Ciprich Subject: Re: consistent LVM snapshot of domUs from dom0 Date: Sat, 8 Dec 2007 22:39:57 +0100 (CET) Message-ID: References: <200712081826.23257.mark.williamson@cl.cam.ac.uk> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Mike Sun Cc: nikola.ciprich@linuxbox.cz, xen-devel@lists.xensource.com, Mark Williamson List-Id: xen-devel@lists.xenproject.org Hi Mike, I think that this problem can be solved using procedure Mark proposed - freeze filesystems of all running domUs using some xm command, then create snapshot and unfreeze them all again. I think that You won't need suspend at all. We just now need to implement it :) n. On Sat, 8 Dec 2007, Mike Sun wrote: > Thanks for the question Nikola and the answer Mark, I was wondering > the same thing. > > Here's another scenario. What if dom0 has a mounted LVM filesystem, > and a file-backed VBD located on that filesystem is used as the root > filesystem by a domU. Would LVM snapshots of the mounted LVM > filesystem provide consistent checkpoints? > > In looking at how xm suspend works, it seems that only memory state is > saved and nothing is done to ensure the guest domain puts its > filesystem into a consistent state, though I'm not completely certain > about that. > > Mike > > On Dec 8, 2007 1:26 PM, Mark Williamson wrote: >>> I'd like to ask a question regarding LVM snapshots: >>> normally if You make a snapshot of mounted LVM partition, DM >>> infrastructure handles putting fs into consistent state using VFS >>> infrastructure. BUT, does it work even if I make snapshot of LV used by >>> XEN? >> >> If your LVM is running in dom0 and you snapshot the storage used by a domU >> then, no, it won't snapshot the domU's filesystem automatically. >> >>> If not, I guess it should not be that hard to fix, I guess we just need to >>> notify domU kernel to call needed VFS function to put fs into consistent >>> state prior to creating snapshot. >> >> Yep. >> >>> Can somebody comment on it, eventually correct me if I'm wrong? >> >> You're quite right. I've just had a look at it and it looks quite feasible to >> do this. The obvious simple way to implement it would be to add an xm >> command that causes a domain to freeze its filesystems into a consistent >> state and then return when that is done. >> >> e.g. >> >> xm create mydomain >> xm fs_freeze mydomain >> >> xm fs_unfreeze mydomain >> >> Ideally the backup operation would just take a snapshot e.g. using LVM or >> qcow. With a bit more tools / storage integration we could have an "xm >> safesnapshot" command that would create a coherent snapshot of the disk. >> >> It would be awesome. >> >> 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-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel >> > > --