changed-block-tracking · shipping · also CBT, changed-block tracking

Changed block tracking

Changed block tracking records written regions of a block device relative to a tracking boundary so a backup can select those regions.

Related Observatory article: Changed block tracking on hesela.com

A libvirt checkpoint identifies a change-tracking boundary without capturing guest state. Recovery still needs the backup payload and its required predecessors. Application quiescing is a separate capture decision. [2]

Libvirt associates checkpoint names with per-disk QEMU bitmaps. Before selecting an incremental, its documented checks require an active-image bitmap, a contiguous same-name bitmap subchain, recording state and no inconsistency. Preserve this tracking lineage when changing overlays; a readable disk chain alone is insufficient. [1]

Relations

related

Dirty bitmap, Incremental backup, QCOW2, Storage snapshot, Application quiescing

Citations

1. libvirt: incremental backup internals, checkpoint relationships and bitmap health (accessed 2026-10-28)
2. libvirt: domain state capture, quiescing and checkpoint APIs (accessed 2026-10-28)

JSON: /data/terms/changed-block-tracking.json