Changed Block Tracking

The changed block tracking (CBT) mechanism allows Veeam Plug-in for Xen to reduce the amount of data read from processed VMs, and to increase the speed and efficiency of incremental backups:

• During a full backup session Veeam Plug-in for Xen reads only written data blocks, while unallocated data blocks are filtered out.
• During an incremental backup session, Veeam Plug-in for Xen reads only those data blocks that have changed since the previous backup session.

To detect unallocated and changed data blocks:

1. During the first (full) backup session, Veeam Plug-in for Xen creates a snapshot of a VM using native Xen capabilities.
2. During subsequent sessions, new snapshots are created. Veeam Plug-in for Xen compares the content of the snapshot created during the previous backup session and the snapshot created during the current backup session. This allows Veeam Plug-in for Xen to detect data blocks that have changed since the previous backup session.