MS HyperV 2016 long-waiting feature

skeleton_computer.gifI don’t know about you, but for me, I like the concept of “better late than never”. This is another article about “Windows HyperV 2016” from the CloudOasis blog. In this one, I want to address one of HyperV Server’s new features, called Resilient Change Tracking.

If you have experience with other hypervisors, then you will be familiar with the functionality of this great feature, especially when comes to incremental backups; Change Block Tracking . Does this sound familiar?

Before we get started on how we can use this, let’s be clear on something. There has not been a native feature like this in Microsoft HyperV until now; and yes, it is in the release of HyperV 2016.

What is Change Block Tracking anyway?

Change Block Tracking (CBT) is a backup technology that hypervisor uses to track the blocks changed since the last backup. CBT is a VMware technology introduced on ESX 4.0, and it is used by backup products to perform incremental backups. Using this technology will reduce your incremental backup time window. Only blocks that have changed from the last backup will be backed up in the new backup.

So, how is my HyperV 2016 incremental backup performed?

Thanks to the backup vendors, a driver has been developed and deployed for use during the backup product installation. After it is installed, it will track the changes made between backups, and so will backup only the blocks changed since the last backup.

Why the big excitement with HyperV 2016?

For years, Microsoft HyperV lacked the change block tracking (CBT) technology, and always relied on the backup vendor drivers to provide this functionality. With the release of Windows HyperV 2016, Microsoft finally embedded this great feature, along with many other great new HyperV 2016 features; including a new Microsoft CBT feature called Resilient Change Tracking (RCT).

When using or migrating to Microsoft HyperV 2016, you will notice two new files related to the RCT technology:

  • The Modified Region Table (.MRT) file: This file maintains a record of changes on the disk/storage, allowing the virtual machine (VM) change block tracking to remain intact and not force a full rescan after any unexpected operation. For example, if a power loss event occurs, the MRT file will be used in the recovery process. The MRT file is written in a writethrough mode, and will always have a record of changes on the disk.
  • The Resilient Change Tracking (.RCT) file: This file can grow up to 6MB and will be used in normal operations; such as in migrations of the virtual machine to another host, in Startup, Shutdown, etc. The RCT file is more granular than the MCT file, but is less granular than the memory bitmap.


Up until recently, I was hesitant to use Windows HyperV as my hypervisor; but each major HyperV release brought new features and surprises from Microsoft. In HyperV 2016, the great new feature is the RCT function. I now will be confident that my HyperV host can natively perform my incremental backups, without compromising my backup reliability that can come from using third-party drivers.


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