WARNING: it works only on XenServer 6.5 or later
You can export only the delta between your current VM disks and a previous snapshot (called here the reference). They are called continuous because you'll never export a full backup after the first one.
Full backups can be represented like this:
It means huge files for each backups. Delta backups will only export the difference between the previous backup:
You can imagine to make your first initial full backup during a weekend, and then only delta backups every night. It combines the flexibility of snapshots and the power of full backups, because:
- delta are stored somewhere else than the current VM storage
- they are small
- quick to create
- easy to restore
So, if you want to rollback your VM to a previous state, the cost is only one snapshot on your SR (far less than the rolling snapshot mechanism).
Even if you lost your whole SR or VM, XOA will restore your VM entirely and automatically, at any date of backup.
You can even imagine to use this to backup more often! Because delta will be smaller, and will be always delta's.
They are called continuous because you'll never export a full backup after the first one. We'll merge the oldest delta inside the full:
This way we can go "forward" and remove this oldest VHD after the merge:
Just go inside your "Backup" view, and select Delta Backup. Then, it's like a normal backup.
During a delta backup job, you can avoid saving all disks of the VM. To do that, it's trivial: just edit the VM disk name and add
[NOBAK] before the current name, eg:
data-disk will become
[NOBAK] data-disk (with a space or not after, doesn't matter).
For every following backup, this disk will be now ignored.