[Xen-users] Re: 100% safe way to backup domU: (was Yet another backup)

[Ligesh <myself@xxxxxxxxxx>]

On Sat, Oct 21, 2006 at 04:06:25AM +0100, Mark Williamson wrote:
> > > What I'd like to attempt to setup (based on the feedback I receive) is
> > > the following.
> > >
> > > 1. Pause the domU using "xm pause"
> > > 2. Sync the domU using "xm sysrq"
> > > 3. Use rdiff-backup to make a local backup of the file VBD
> > > 4. Resume the domU using "xm unpause"
> 
> > 1. Pause the domU using "xm pause"
> > 2. Sync the domU using "xm sysrq"
> > 3. Use LVM to snapshot to LV providing the VBD to the DomU
> > 4. Resume the domU using "xm unpause"
> > 5. Use rdiff-backup to make a local backup of the snapshot LV
> > 6. Remove the snapshot
> 
> You're both going to have to change the sync-ing stage to come before the 
> pause - otherwise the domain won't be running and therefore won't be able to 
> sync it's disks!
> 

 In that case we need a command for xm called 'sync-and-pause'. I had actually 
come up with the same plan, and it seems to be the only way to take safe 
backups. If there were a delay between the sync and pause, we are not really 
gaining true peace of mind. You need to sync the domain after it is paused or 
it should be done as an atomic action. As a matter of fact, the steps the below 
actually constitutes a 100% safe way to backup the domain, and will make Xen 
better than openvz as far as hosting is concerned. One of the main concerns for 
a provider is daily backups, and with Xen the chance of corruption is very 
high, while with the openvz single kernel architecture, the issue is only 
application memory caches which can be recovered individually. But with the 
setup below, we finally have a breakthrough. (At least for me).

 xm sync-and-pause domU
 lvm snapshot domU
 xm unpause domU

 Thanks.



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