Re: [Xen-users] snapshot - backup for xen vm's

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Fajar A. Nugraha wrote:
> it-news (Josef Lahmer) wrote:
>   
> > is there a way to make a lvm-snapshot of an running xen-vm to implement a function like 
> > "snapshot-backup"?
> >
> > #) make snapshot
> > #) mount snapshot
> > #) copy files
> > #) umount snapshot
> > #) remove snapshot
> >
> > eg (http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html)
> >
> > regards
> > josy
> >
> > interessting: How to mount a XenVM filesystem on XenServer Host:
> > http://kb.xensource.com/entry.jspa?categoryID=14&externalID=162
> >
> >   
> >     
> If you :
> - use an LV (NOT files) on dom0 as storage for domU's block device
> - use partitions on domU (NOT LVM)
>
> Then both link are applicable right away, in the sense that :
> - you create an LVM-snapshot of the LV used by domU
> - use kpartx to create block device nodes for partitions on that
> LVM-snapshot
> - mount the partitions
> - copy files
> - umount partitions
> - remove LVM snapshot
>
> Personally, I prefer using dom0-LVM directly as partitions on domU (i.e.
> all partitioning and LVM is handled by dom0). But that will also mean I
> can't install domU using Anaconda (in the case of RHEL), I have to
> manually copy it form an exisisting physical machine.
> yum --installroot should work, but you need to do some extra
> configurations afterwards.
> Yast install to directory on SUSE should also work.
>   
Unfortunately, that piece of over-hyped installatiion obscurity known as 
libvirt does not allow you options to do this, and mandates the use of 
pygrub. This means that you must have a /dev/xdva device, and grub 
itself only works if you have a disk, not if you only have partitions.
Anaconda is also not your friend: but it's possible to do RPM or yum 
installs into a target directory to build your initial OS images on a 
partition, edit your configuration files there, and boot that. Just 
beware that "touch" commands in certain RPM post-install scripts will 
hang and need to be slapped in the head to allow the yum installation to 
complete.
I'll publish my widget for this when I have a few cycles. It's also 
very, very helpful to have enough disk in the partiton to mirror the 
*whole* RedHat or Fedora installation directory. But doing things this 
way also allows you to do all your updates at the same time, with a 
chroot command, which I consider a *huge* bonus.
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