Re: [Xen-users] Fw: coordinating VM snapshot with LVM snapshot.

[J Nb <j_nwb@xxxxxxxxx>]

I will look in to XCP.. but my guess is that they use their pv drivers to 
communicate via xenstore..etc. I am looking for something that would work with 
vanilla open source xen. (well non XCP  :) )

But my plan is same as I described in skeleton and organization very similar to 
yours. but to have something that works with ssh/wmi. This way scripts etc can 
be centrally managed.

What I was looking for was 
 -- For xen is there a flush command for PV and HVM vms. (hypervisor level)
 -- Is sync sufficient as a starting point at OS level.
 -- Any repository of application specific scripts. (Mysql,oracle..etc)
 -- And anything to control cpu/io consumption of the backup process. (Probably 
start with cstream / nice)

-nb

--- On Thu, 1/14/10, Pasi Kärkkäinen <pasik@xxxxxx> wrote:

> From: Pasi Kärkkäinen <pasik@xxxxxx>
> Subject: Re: [Xen-users] Fw: coordinating VM snapshot with LVM snapshot.
> To: "J Nb" <j_nwb@xxxxxxxxx>
> Cc: "xen-users" <xen-users@xxxxxxxxxxxxxxxxxxx>
> Date: Thursday, January 14, 2010, 9:15 AM
> On Wed, Jan 13, 2010 at 09:11:47AM
> +0200, Pasi Kärkkäinen wrote:
> > On Tue, Jan 12, 2010 at 05:44:18PM -0800, J Nb wrote:
> > > Anyone ?
> > > 
> > 
> > Now that XenServer is opensourced as XCP (Xen Cloud
> Platform), you could
> > take a look at the source.. 
> > 
> > I believe XenServer supports Windows VSS coordination
> for snapshots.
> > "xe vm-snapshot-with-quiesce"
> > 
> 
> Did you get anywhere with this? 
> 
> For a long time I've been thinking of writing some kind of
> 
> "VSS" library/daemon for Linux.. similar to Microsoft
> Windows 
> Volume Snapshot Services.
> 
> It could (and should) be called something different than
> VSS, 
> but I'll just use that name for now..
> 
> The interface/usage could be something like:
> 
>     1. backup begins
>     2. execute in the guest: "vss_control
> pre-snapshot xvda"
>     3. take snapshot of the lvm volume
> having guest disk xvda
>     4. execute in the guest: "vss_control
> post-snapshot xvda"
>     5. do the actual backup from the lvm
> snapshot
>     6. backup ends
> 
> This would have minimal downtime for the applications
> running in the guest.
> 
> pre-snapshot action would go through all the application
> specific pre-scripts, 
> execute them, preparing the applications for taking the
> snapshot, and then 
> it would flush the filesystem, kernel and disk caches as
> needed to prepare for
> a consistent snapshot.
> 
> Preparing the application for taking the snapshot might
> mean something
> like placing locks to database tables preventing disk
> writes from happening, 
> or shutting down the application, or whatever the specific
> application requires.
> 
> post-snapshot action would again go through and execute all
> the application specific
> post-scripts releasing the applications back to normal
> running state.
> 
> The application specific pre/post scripts could be stored
> like this:
> 
>      
> /etc/vss/scripts/xvda/001-mysql.pre
>     /etc/vss/scripts/xvda/001-mysql.post
> 
>     /etc/vss/scripts/xvda/002-pgsql.pre
>     /etc/vss/scripts/xvda/002-pgsql.post
> 
>    
> /etc/vss/scripts/xvda/003-my_custom_app.pre
>    
> /etc/vss/scripts/xvda/003-my_custom_app.post
> 
> Or you could have "scripts/xvda2/*" if you have lvm volumes
> directly as
> partitions to the guest. You get the idea.
> 
> Then the next step would be to create a daemon ("vssd")
> that listens for
> requests from the network, and/or possibly from Xen dom0
> through the hypervisor.
> 
> Or then the backup server might issue those pre-snapshot
> and post-snapshot 
> commands through ssh.. many options how to implement it.
> 
> Does this make any sense? Comments?
> 
> -- Pasi
> 
> > 
> > > 
> > > --- On Sun, 1/3/10, J Nb <j_nwb@xxxxxxxxx>
> wrote:
> > > 
> > > > From: J Nb <j_nwb@xxxxxxxxx>
> > > > Subject: coordinating VM snapshot with LVM
> snapshot.
> > > > To: xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > Date: Sunday, January 3, 2010, 6:17 PM
> > > > Hi
> > > >    How to co-ordinate VM snapshots and
> disk
> > > > snapshots ? Here is a sequence I am thinking
> of
> > > > automating...
> > > > 
> > > >   1.Tell VM to sync (say via ssh or some
> special
> > > > agent)
> > > >      * This will do "sync" and any
> > > > application specific hook to make it
> quiescent.
> > > > 
> > > >   2. Tell VM/Hypervisor to flush all disk
> buferes
> > > > ?  (HOW ??? )
> > > >      * Anything at this level?
> > > > 
> > > >   3. Pause the VM
> > > > 
> > > >   4. xm save -c (To save the VMs state in
> to
> > > > checkpoint file.)
> > > >       (This may take more time !)
> > > > 
> > > >   5. Take LVM snapshot for each disk. 
> > > > 
> > > >   6. Unpause the VM
> > > > 
> > > >   7. Application level resume if any.
> > > >   
> > > >   7. Use the snapshot to copy each disks
> ?!!!! (either
> > > > dd or mount followed by cp/rsync)  (This
> can be big!
> > > > Any optimization suggestions )   
> > > > 
> > > >   8. discard snapshot.
> > > > 
> > > > 
> > > > Would the above sequence work ? 
> > > > 
> > > > Any suggestions on individual steps ?
> > > > 
> > > > Anything specific for PV and HVM virtual
> machines?
> > > > 
> > > > Is there a backdoor to qemu-dm console ?
> > > > 
> > > > Does anyone know how similar functionality
> is implemented
> > > > in XenServer product or Virtual Iron or
> anyone else? 
> > > > 
> > > > -nb
> > > > 
> > > > 
> > > >       
> > > > 
> > > 
> 
> 
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