[RFC Doc V11 1/5] domain snapshot terms

[Chunyan Liu <cyliu@suse.com>]

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Terminology

* Active domain: domain created and started
                 (also referred as "live")

* Inactive domain: domain created but not started
                 (also referred as "offline")

* Domain snapshot:

  Domain snapshot is a system checkpoint of a domain. It contains
  the memory status at the checkpoint and the disk status.

* Disk-only snapshot:

  Disk-only snapshot only keeps the status of disk, not saving
  memory status.

  Contents of disks (whether a subset or all disks associated with
  the domain) are saved at a given point of time, and can be restored
  back to that state. On a running guest, a disk-only snapshot is
  likely to be only crash-consistent rather than clean (that is, it
  represents the state of the disk on a sudden power outage); on an
  inactive guest, a disk-only snapshot is clean if the disks were
  clean when the guest was last shut down.

* Live Snapshot:

  Like live migration, it will increase size of the memory dump file,
  but reducess downtime of the guest.

* Internal Disk Snapshot

  File formats such as qcow2 track both the snapshot and changes
  since the snapshot in a single file.

* External Disk Snapshot

  The snapshot is one file, and the changes since the snapshot
  are in another file.