Re: [Qemu-devel] Correct syntax for named snapshots

[Philipp Hahn <hahn@univention.de>]

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Hello Ottaavio,

On Wednesday 26 October 2011 18:24:01 Ottavio wrote:
> According to the latest doc file you create a named snapshot like this:
>
> qemu-img snapshot [-l | -a snapshot | -c snapshot | -d snapshot]
> base-image.img
>
> Is this other following syntax still supported or deprecated:
>
> "qemu-img create -f qcow2 -b base-image.img snapshot.img"  ?

These are two different things:
The first one creates an *internal* snapshot, which is stored internally in a 
*single* qcow2 file.
The second one creates an *external* snapshot, which creates a *new second* 
qcow2 file.

The first functionality requires a lot more work for qcow2, which can easily 
corrupt your qcow2 file if something goes wrong. Because of this QED (one 
follow-up format of Qcow) IMHO dropped support for internal snapshots.
The second variante has the drawback, that for each snapshot your get an 
additional file, which your have to manage. Deleting one file from the middle 
of such a chain breaks all following snapshots, so be careful when you do 
delete files.

And yes, both are still supported.

Sincerely
Philipp
-- 
Philipp Hahn           Open Source Software Engineer      hahn@univention.de
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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