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Update delta_backups.md

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Olivier Lambert 2015-12-18 18:02:19 +01:00
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delta_backups.md
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# Delta backups
> This feature will be out when delta VHDs will be officially supported by Citrix, in XenServer (Dundee).
> This feature is out since 4.11
The next version of XenServer will support delta VHD export. It means you can export only the delta between your current VM disks and a previous snapshot (called here the *reference*).
> WARNING: it works only on XenServer 6.5 or later
It's very similar to VEEAM *Forward Incremental Backup*, as explained in [their documentation](http://helpcenter.veeam.com/backup/80/hyperv/forward_incremental_backup.html):
You can export only the delta between your current VM disks and a previous snapshot (called here the *reference*).
![](https://xen-orchestra.com/assets/delta.png)
Full backups can be represented like this:
![](https://xen-orchestra.com/blog/content/images/2015/12/nodelta.png)
It means huge files for each backups. Delta backups will only export the difference between the previous backup:
![](https://xen-orchestra.com/blog/content/images/2015/12/delta_final.png)
Basically, you'll create "key" backups (full backup) and use delta from those. It's the same principle for [MPEG compression and key frame](https://en.wikipedia.org/wiki/Key_frame#Video_compression).
@ -14,14 +20,9 @@ You can imagine to make a full backup during a weekend, and only delta backups e
* 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](rolling_snapshot.md) mechanism).
Even if you lost your whole SR or VM, you can use a Full backup to restore it completely, then apply any existing delta on top!
## Challenges
* XenServer delta VHD support
* GUI to restore in one click multiples *.vhd files
* The "key" snapshot must NOT be deleted by the user
Even if you lost your whole SR or VM, you can use a Full backup to restore it completely, then apply any existing delta on top!