On Thu, Jan 14, 2010 at 10:34:30AM -0800, J Nb wrote:
> 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 :) )
>
Yeah.. most probably.
> 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.
>
Indeed.
> What I was looking for was
> -- For xen is there a flush command for PV and HVM vms. (hypervisor level)
>
Not that I know of. If you use phy: backend for LVM volumes, then dom0
doesn't do any caching.. then it's enough to flush the caches and disks in
the guest.
> -- Is sync sufficient as a starting point at OS level.
>
I'm not sure.. Linux kernel v2.6.29 added filesystem "freeze" feature
(http://lwn.net/Articles/287435/) that can possibly help here.
I remember reading that "sync" might not really flush everything.. but
yeah, I guess it's good enough as a starting point.
> -- Any repository of application specific scripts. (Mysql,oracle..etc)
>
Do you mean a website with scripts to share with others? Ideally
application specific scripts would be packaged together with the apps,
assuming this kind of "vssd" was included as a default in the distros :)
> -- And anything to control cpu/io consumption of the backup process.
> (Probably start with cstream / nice)
>
This pretty much depends where you do the snapshots and from where you run
the backups.. and also on the used storage solution.
-- Pasi
> -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
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> >
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
> >
>
>
>
>
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