Re: [Qemu-devel] [RFC] qemu snapshot enchancement

[Dietmar Maurer]

> >>     Thanks for declaration, one more question:
> >> 3) will have a big image file, will you back up it or just leave it
> >> there, not backup for internal snapshot?
> >
> > Sorry, I do not understand that question. Why will I have a 'a big
> > image file', and what do you mean by 'backup' exactly?
> >
> 
> To make data safe, I guess usually there would be two copy of image data,
> one is the VM used, one is on another "data restore server".
> There are choices about how to store the data:
> One is do a full clone of image disk, at each time user want to protect his
> data.
> One is only do a full lone of image disk at first time, later at each time, 
> only
> copy out the delta data, which is obvious better.

Again, I would not mix "VM backup" and "VM snapshots". This is something 
different,
and it is very confusing to mix them.

But yes, in general there is 'full backup', and 'incremental backup' (delta).
But IMHO 'incremental backup' is not obviously better.

I currently also thing about storing backups to some dedup database - then you 
can
have full backups with space requirements of incremental backups. 

> internal snapshot increase the image file size, for eg, after internal 
> snapshot
> 10G image will become 10.1G, and it seems no way to get the 100M delta
> data and store it in "data restore server", so you will have do a clone of
> 10.1G data again. So I asked whether you have done a "snapshot data copy
> to restore server" in the following.

Our current backup tool always stores the current data, so any snapshot data is
not contained in the backups.

Note: The proposed backup patches (already sent to the list) make backups 
without
creating internal/external snapshot. Consistency is guaranteed by using COW.