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Add Changed Block Tracking (CBT) support - #4
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CBT turned out to need no NFC reverse engineering at all: VirtualMachine.QueryChangedDiskAreas -- the actual changed-byte-range query real backup tools use, distinct from VDDK's own VixDiskLib_QueryAllocatedBlocks (a different, disk-internal allocated-block bitmap) -- is public VIM API with no VDDK/NFC involvement whatsoever. Adds thin wrappers: enable_change_tracking (sets changeTrackingEnabled via ReconfigVM_Task), disk_change_id (reads a disk's current changeId off its backing, once CBT is active and a snapshot exists), and query_changed_disk_areas (the actual changed- range query, converted to plain dataclasses). Also documents real-world characteristics found through live testing, not obvious from the API docs: - A wildcard changeId="*" query (the initial-full-backup path) reports only *allocated* regions on a thin-provisioned disk, not the full sparse virtual capacity. - A single large contiguous write comes back as one extent regardless of size; only the number of *discontiguous* changed regions drives how large the extent list gets -- the real scaling risk for CBT on a busy disk is fragmented random I/O, not big sequential writes. Adds unit tests (ValueError paths, VIM call argument/result conversion, mocked -- no lab needed) and an integration test exercising the full cycle: enable CBT, snapshot, write a known sector, snapshot, query, verify the write falls inside the reported extent. Validated against a live standalone ESXi 8.0.3 host. Full workflow and lab evidence: docs/cbt.md.
Keep the merged NFC features and add Changed Block Tracking.
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Collected from cloudbase#6
Original author: doccaz
Original branch:
pr4-cbtThis pull request is the open upstream change, retargeted at
replication_agent.Changed Block Tracking uses the public VIM API (
enable_change_tracking,disk_change_id,query_changed_disk_areas), not an NFC message.