Re: [Xen-devel] [RFC V9 1/4] domain snapshot terms

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-12-16 at 14:32 +0800, Chunyan Liu wrote:
> Changes to V8:
>   * add a document for domain snapshot related terms, they will be
>     referred in later documents.
> 
> =====================================================================
> Terms
> 
> * Active domain: domain created and started
> 
> * Inactive domain: domain created but not started

As Wei says I think you mean "defined" here, since created and started
are (essentially) synonyms for some toolstacks.

You'll probably want to define "defined" too for clarity.

> 
> * 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.

There is the possibility of doing clean snapshots if a guest agent is
involved to quiesce the disks at the right moment (e.g. I believe qemu
has such a thing, or at least I've seen talks about it being developed
at conferences). Are you including this possibility or explicitly ruling
it out of scope?

> * 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.



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