How Block-Level Backups on UNIX Work

Article ID: DAPR0009 How Block-Level Backups on UNIX Work

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How Block-Level Backups on UNIX Work

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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 native (CVBF/LVMs) backup operations, both the 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.

    For native disks, CVBF snapshots are taken. The snapshots are created in the /dev/CVBF directory.

    For native LVMs, Commvault uses the LVM snapshot capability for snapshot creation.

    For hardware backups, Commvault uses the vendor-specific snapshots.

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

  2. Scan sub-phase: If you enabled metadata collection at the subclient level, then file-level collect files are generated.
  3. Catalog sub-phase: The file-level metadata is collected. The volume bitmaps and the block device config file are uploaded to the index.
  4. Archive index sub-phase: The index for the backup job is backed up to the media.
  5. Cleanup sub-phase: The temporary files that were created under 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 native backup operations, a spool copy is automatically configured, and the snapshots are deleted after the backup copy job runs. For hardware backups, the snapshots are deleted according to the storage policy settings.