XenServer incremental backup

Backup Dec 18, 2015

Yaay! It's now possible make incremental (or delta) backups in XenServer, and in an easy way. Thanks to Xen Orchestra :) Let's explore this great feature!

Note: this feature is only available from XenServer 6.5[^n]

Until now

We already got 3 ways to rollback or backup your current XenServer VMs:

A "real" backup (ie: be able to recover your VMs even by losing all your storage or host) is only possible with the first 2 options. Indeed, snapshots are not really a backup solution, it's a rollback solution: if you lose your SR, your snapshots are lost too!

But space usage of full rolling backup can be a real concern. Let's use an example!

Example

You want to backup a VM named WindowsServer_A. This VM has a 500GB disk, with a real usage of 100GB.

If you want to backup every night of the week with a retention of 7, it will be something like this on your backup storage:

7 full copies of your VM. Let's do the maths, because each .xva file will use ~100GB: it's 700GB of disk used only for this VM. At worst, during the retention of the 8th backup, you'll use 800GB of disk (time to write the 8th backup, then remove the oldest one).

Let's see then how it works using XO delta backup! (which is the feature name for XenServer incremental backup!)

XO delta backup

By using the new capabilities of XenServer 6.5 (VHD export), we can considerably reduce the size of backups. And keeping the same level of backup for the administrator!

The first export will be a full backup too
Then, we'll export only incremental data from this VM (delta from previous... delta)
We'll cycle to offer the same retention policy

delta_final

From the previous example, let's imagine you modify 1GB of data on your VM everyday. You'll use only 106GB of disk. Even in the worst case scenario (8th backup), the difference will be almost 600GB saved for the same backup service!

But that's not all! You'll also save a considerable amount of time for your VM backup: exporting 1GB is not the same as exporting 100GB. Thus, it opens the possibility to make backup more often.

To create them, just go inside the Backup menu and select "Delta Backup":

Restore a delta backup

That's exactly the same than restoring a full backup: nothing changes! Just go inside the "Restore" view, select the VM you want to import and from which backup (also choose the target Storage to import it). That's it!

You can import it on any SR, even a freshly installed XenServer host: all the VM data will be restored!

More to come!

This feature is just a start! We can start to work now on two things to improve Xen Orchestra:

improve the delta to avoid any new full export, even after the retention number is exceeded
use those delta feature to improve Disaster Recovery feature: this could lead to a near-realtime replication on a remote host!

Forever incremental backup

Does this name ring any bell? Yes, that's the VEEAM solution to avoid any full export after the first one. By merging the older full backup to the oldest delta, we could achieve this. Be sure we'll work on this very soon!