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

To: "Fajar A. Nugraha" <fajar@xxxxxxxxxxxxx>
Subject: Re: [Xen-users] snapshot - backup for xen vm's
From: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
Date: Fri, 25 May 2007 04:25:50 +0100
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Fajar A. Nugraha wrote:
Nico Kadel-Garcia wrote:
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"?

[snip]
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
[snip]
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.
pygrub works perfectly with partition-only setup (at least on RHEL5).
You could take a virt-manager-based installation, copy the files to
partition-only-domU setup, modify grub.conf and fstab, and have a
working system.

I know this seems like an extra unnecessary step (install-copy-modify
instead of just install). Which is why my prefered method is to create a
template (in tar.gz, with some host-specific stuff like ssh host key
removed), so the next "installation" can simply be a tar xvfz.
It is a painful extra step. Pygrub doesn't read the MBR off of the para-virtualized image?

I've used the "jailtime" tarballs for CentOS: they're fairly reasonable, but are cluttered with disk images rather than simply providing a tarball and letting the installer set up their own partitions.

 It's also very, very helpful to have enough disk in the partiton to
mirror the *whole* RedHat or Fedora installation directory.
I'm not sure what you mean here. I'd prefer to have a local copy of yum
repository (including RH installation directory). It's on local network,
accessed via http, but it doesn't have to be on dom0. That way it scales
well if you have lots of dom0s.

Regards,

Fajar
Mirror the whole RedHat DVD or network install site. Copy it to local disk on the domain creating machine: you want this all to happen on local disk, *NOT* over a network! Make a new partition, and mount it. Copy the whole thing over to /var/cache/yum/base/packages and work from there to install whatever you want, usually with yum. Do an alternative root directory RPM or Yum installation into that directory. But using yum, it downloads the files: it's vastly faster to simply copy them over and use a "file:///" based URL, rather than the classic HTTP or FTP URL's. be already available or wind up downloaded into /var/cache/yum in the target directory, but you have a huge advantage in being able to do the updates or add-on packages at OS image install time, rather than wending your way through

Some folks try to set up teeny-tiny little Xen partitions for firewalls or other resource limited setups, so they might not have the space to do this stunt comfortably.

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