Imagine you are casually sitting at your desk, working on some vital report, when your cat decides to bump into your coffee and spill it all over your laptop (probably on purpose). ZAP! Your report is lost forever and hours of your time have been wasted.

Now imagine that instead of using your plain old laptop, you are using a virtual desktop from XenDesktop, running on XenServer. In this case, your broken laptop doesn’t matter, as your data is stored in a data center (safely out of your cat’s reach). This, however, brings some new risks, as a single data center failure could result in many users losing their data. To stop this from happening, it is essential that we have regular backups to which we can revert.

XenServer has always had the ability for administrators to export virtual machines. However, you probably don’t update every block of data on your VM’s disk every night, and instead, want to export only the changes since the day before. Quite apart from the space needed on your backup target, how long it takes to copy a full disk across can be problematic; after all, all your VMs need to complete the backup operation in one night!

Introducing Changed Block Tracking

To address this, XenServer 7.3 introduces Changed Block Tracking (CBT) backup APIs. These allow your backup software to:

  • Identify and backup only the data that has changed since the last backup, so you are no longer required to export the whole disk each time. This means backups are much faster and can be done more regularly.
  • Delete snapshot data after a backup (leaving behind only the metadata) so that less space on your host is used up.
  • Pick up from where you left off in a backup in the case of a transfer failure.
  • Easily integrate backup software with XenServer.

On average, only 10% of blocks change between each backup so by using Changed Block Tracking you can cut your backup time in half compared to exporting the VM’s whole disk. This benefit increases even further if you backup more frequently so that for customers who backup hourly the entire process may take only a few minutes.

Our certified software partners that already support XenServer CBT include:

SEP SESAM, releasing March 2018

SEP Sesam has protected Citrix XenServer since version 5.6 via certified Citrix API. With its upcoming release, SEP sesam Grolar offers comprehensive backup and recovery support of the enhanced Citrix API of Citrix XenServer 7.3 including CBT (Change Block Tracking).

Quadric Alike v4.6.2, released in December 2017

Quadric Software’s Alike offers complete protection for both Citrix XenServer and Microsoft Hyper-V environments. 


Storware vProtect, released in December 2017

Storware vProtect is an enterprise backup solution for virtual environments that facilitates the implementation of virtual machine backup running on open platforms such as Citrix XenServer.

Want to Try CBT Out?

We know that you will love the benefits the CBT brings, so why not give it a try? To use CBT, you need to have XenServer Enterprise Edition (or be entitled to that via a XenDesktop/XenApp license) and CBT-compatible backup software. If needed, you can obtain a 90-day trial of XenServer Enterprise Edition.

Interested in Developing with CBT?

In addition to software from our partners, you can also find some open-source projects which utilise CBT:

  • A complete backup program written by one of the engineers who helped to create CBT can be found here.
  • A set of examples on how to use the CBT APIs for end-to-end backup and restoration can be found here.
  • The developers guide for integrating Changed Block Tracking into your backup solution can be found here.