How Block-Level Backups on Windows Work

Specifying the Volume to Back Up

To perform block-level backup operations on a snapshot-capable volume, configure the volume as subclient content. The volume that you back up can be a from a local disk or from a hardware snapshot engine that is supported by Commvault.

The Phases of Block-Level Backup Operations

Block-level backup operations have the following phases:

• Snapshot copy phase
• Backup copy phase

Both of these phases have several sub-phases. For Commvault native engine backup operations, both phases run as a single job. For hardware snapshots, the snapshot copy phase and the backup copy phase run separately as two jobs.

Snapshot Copy Sub-Phases

1. Backup sub-phase: A snapshot is created as follows:

• For Commvault native engine backups, Commvault uses the Volume Shadow Copy Service (VSS) to create the snapshot.
• For hardware backups, Commvault uses the vendor-specific snapshot engines to create the snapshot.

The QSnap driver monitors the device and creates a bitmap by tracking the changed blocks, while writes are performed on the volume that is being monitored. A block device config file, which holds the volume details and properties, is also created.

1. Cleanup sub-phase: The temporary files that were created in the Job Results directory are removed.

Backup Copy Sub-Phases

1. Scan sub-phase: The volume bitmaps and the block device config file are downloaded from the index. Extent collect files that have data-only blocks are generated.
2. Backup sub-phase: The snapshots are mounted, and the extents are moved from the snapshot to the media.
3. Archive index sub-phase: The index for the backup job is backed up to the media.

For Commvault native engine backups, a spool copy is automatically configured. After the backup copy job runs, the snapshots are deleted. For hardware backups, the snapshots are deleted according to the storage policy settings.

File Indexing After Block-Level Backup Job Completion

If you enable the Index files after backup option, files are cataloged offline as a separate job after the block-level backup completes.