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Re: [Xen-users] How to list the drives a DomU is using, and their types -- with or without a parition -- from the Dom0?

  • To: xen-users@xxxxxxxxxxxxx
  • From: "Austin S. Hemmelgarn" <ahferroin7@xxxxxxxxx>
  • Date: Tue, 16 Feb 2016 12:04:27 -0500
  • Delivery-date: Tue, 16 Feb 2016 17:06:19 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

On 2016-02-16 10:47, billb@xxxxxxx wrote:

On Tue, Feb 16, 2016, at 07:06 AM, Simon Hobson wrote:
Personally, I work the other way - I do backups from within the guest using 
rsync to maintain a clone of the filesystem as seen
That thread also suggests

"Run a backup daemon inside the guest instead.  There are plenty of
network backup programs around.  Choose your favorite one and install
it in your VM."

which I think is what you're saying you're doing.
In general this is more scalable than doing all the work in Domain-0, and has the advantage that it decouples the backup from the underlying hardware/hypervisor, which means you can more easily restore on a different configuration (be it a different hypervisor, different storage configuration, or even on physical hardware if the need arises). If you really want to manage backups from Dom0 though, my suggestion would be to use something like Ansible or Puppet to dispatch to the individual guest systems. I've got my systems set up with Ansible so that Domain-0 calls out to each individual guest system to run the backup using their resources, and then copy it over to Domain-0 to then move to archival storage (in my case, a local near-line RAID array, and Amazon S3). This means I don't have to fight with LVM snapshots (which are dangerous for my use case, because I use BTRFS for most of my systems), can serialize the backups however I want, take advantage of the page cache in each guest (trashing the cache has almost zero impact on my workloads, and part of the stuff I need to read in cache already saves I/O time), and have less overall impact on any given guest while the backup is running in a different guest.
* It's worth considering the way snapshots work.
Yep.  Sound like there are some issues to worry about.

It'd be great if there was an approved/recommended, safe & well documented way to make  
point in time "snapshots" (or whatever you'd call them) of Xen guests.  If it's 
there in the docs I didn't get to it yet.

I'm after two things.

1st, general regular backups of production guests.
This is better done with regular backup software, as that can handle many things that a straight snapshot can't, like specific exclusions for filesystem based caches.

and 2nd, snapshots at various stages of guests' installs that I can store away somewhere, 
and use to quickly spin-up a new guest in a "pre configured" state.
LVM snapshots are good for this however, and I'd say you're better off just using disk images instead of backups of individual filesystems. You may want to look into something like partimage if space usage is a concern and you have to keep disk images separate form the LVM snapshots.

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