You receive an e-mail notification with backup log, containing one or multiple lines with "Volume Tracker has failed to find changes on volume..."


2018-12-20T09:00:10:378-04:00 10916 I000101F8: Pending operation 173 started: 'Creating partition image'.


2018-12-20T09:00:11:190-04:00 10916 I00100000: Volume Tracker has failed to find changes on volume '\\?\Volume{5e2aeab2-ffb3-4dab-8444-54635f6a3367}\'.


When backing up a Hyper-V Virtual Machine running on Windows Hyper-V Server 2016 (Windows 10) or higher AND this Virtual Machine is running on outdated VM configuration version 5.0, then Changed Block Tracking information for this virtual machine cannot be retrieved and entire virtual disks are processed during backup. 

Example of backup log where the problem is observed – both virtual disks are read from start to end instead of reading only changed sectors reported by CBT:

You have 2 or more backup plans applied to a Hyper-V virtual machine. You notice that backups start taking much time.

When you check the service process logs for the affected plan, you see the following records, where "bytes read" values are too high and nearly match the total size of the virtual disk:

2019-10-03T23:39:48:564+07:00 6304 I00000000: I/O statistics for device 'VM(IFACE_ATA0:0)': 109139525632 bytes read, 0 bytes written.


1. You back up a Windows machine,
2. Backup finishes with warning "Volume Tracker has failed to freeze checkpoint. A device attached to the system is not functioning"