[sheepdog-users] Snashot and backup

[Liu Yuan]

On 12/06/2012 10:01 PM, Valerio Pachera wrote:
> Hi all, may anybody write me same examples on how to backup a vdi disk?
> I've been looking for documentation but I didn't find anything.
> 

what do you mean by 'backup a vdi'?

If you mean reading it from Sheepdog cluster and store it as a local
image, you can actually convert it by:

$ qemu-img sheepdog:image -O format(such as qcow2) backup_name

Then you can see a image named backup_name on your local disk. I assume
you meant this kind of 'backup'. Actually we have another 'collie vdi
backup' to backup only the differential data between snapshots. See more at
http://lists.wpkg.org/pipermail/sheepdog/2012-September/006771.html

> To backup a vdi disk:
>   1) the guest that uses it has to be off

The guest has to be off to get a consistent 'backup', though you can
convert it on the fly. (I am not sure about this because I never try to
convert a image when it is running).

>   2) the guest may be running but it's better if it's off
>   3) it doesn't matter if it's running or not
> 
> Backup can be don only from a snapshot?
>   True or False
> 

False.

You can convert whatever images you see in the 'collie vdi list'

> Backup is never intend like a copy of a file that I can store elsewhere.
> I'm used to make copies of file (.qcow / .raw) or block devices (dd of
> a logival volume) to a nas.
> With sheepdog a copy is still inside the cluster, there's no way to
> 'export' a vdi disk to an external storage.
> Is that right?
> 

Nope.

Besides 'qemu-img convert', we can also use 'vdi
read/write/setattr/getattr' the sheepdog images.

You can even mount those images locally via sheepfs.

> I made a clone of a snapshot of the vdi named 'squeeze'.
> From vdi list I saw
> ---
>   Name        Id    Size    Used  Shared    Creation time   VDI id  Copies  Tag
> c squeeze_clone     1   10 GB  152 MB  2.6 GB 2012-12-06 14:49    d8d65     2
> ---
> 
> Later I 'c' has gone away.
> ---
>   squeeze_clone     2   10 GB  0.0 MB  2.7 GB 2012-12-06 14:57    d8d66     2
> ---
> 
> When is the 'c' going away?
> 

What did you do between the time it went away? I can't reproduce the
problem. The 'c' indicator always hangs there on my box

Thanks,
Yuan