[virt-tools-list] Best way to backup my VMs

[Christian Grassi]

Actually you create a doubt in my mind...
If you have a VM with lots of memory, if you just suspend the machine,
and back it up without saving the ram, in teory, as no fsync succeded
you could lose a lot of stuff which is in the filesystem cache and not
synced.
Am I wrong ?

Regards

Chris
On Tue, 2011-04-12 at 17:50 +0200, Frédéric Grelot wrote:
> > Actually, this isn't right.  Think about the case where you lose
> > power to
> > your computer; you don't get corrupted disks, you get
> > "crash-consistent" disks
> > (this is what journaling filesystems are for).  So if you know what
> > you are
> > doing, it is sufficient just to pause the guest (virsh suspend
> > <guest>), take
> > the backup, and then resume the guest (virsh resume <guest>).  True,
> > you
> > won't get all of the data that might have been in-flight in memory,
> > but it
> > should be a valid state of the disk.
> 
> I tend to agree with that, it already happened to me for a zimbra server, and I lost nothing.
> 
> > 
> > That all being said, installing backup software in the guest is the
> > best
> > course of action.
> 
> An other method to profit from virtualization-enabled server would be to take the following actions :
> -inside guest : turn of server application
> -inside guest : unmount data disk
> -host : pause guest (necessary?)
> -host : lvm (or qcow/qed) snapshot of disk
> -host : resume guest
> -inside guest : remount and restart server application
> 
> Provided there is no side-effect of unmounting with regard to guest cache (to be confirmed), I think this would reduce downtime, and permits backup of specific parts of the server application without stopping it as a whole.
> A (maybe safest) other option would be to gracefully shutdown the server, LVM/qcow/qed snapshot its disk and restart the server immediately : the data duplication itself won't account for the downtime, since it can be done later.
> 
> Frederic.
> 
> > 
> > --
> > Chris Lalancette
> > 
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