Re: [Qemu-devel] [RFC] RFC on Backup tool

[Stefan Hajnoczi]

On Tue, Jul 18, 2017 at 05:29:11PM -0400, John Snow wrote:
> 
> 
> On 07/17/2017 03:37 PM, Ishani wrote:
> > ----- On Jul 17, 2017, at 12:48 PM, Fam Zheng address@hidden wrote:
> >> On Sun, 07/16 02:13, Ishani Chugh wrote:
> 
> [...]
> 
> >> Only full backup is implemented in this patch, is the plan to add 
> >> incremental
> >> backup on top?  I'm curious because you have target file path set during 
> >> drive
> >> add, but in the incremental case, it should be possible that each backup 
> >> creates
> >> a new target file that chains up with earlier ones, so I think the target 
> >> file
> >> should be an option for "backup" command as well.
> > 
> > Yes. Incremental backup is to be added. I am still in learning phase with
> > respect to incremental backups. I will modify the arguments and workflow 
> > accordingly.
> > 
> 
> You may consider solidifying the backup target *pattern* during drive
> add as an alternative, such as:
> 
> .../path/to/backup/%VM%/%DRIVE%/%yyyy%-%mm%-%dd%.qcow2
> 
> Or some such scheme. Simple numerals work well, too:
> 
> myvm/sda/incr.0.qcow2
> myvm/sda/incr.1.qcow2
> 
> Simple numerals offer the benefit that it is easier to reconstruct the
> chain if you lose your metadata in the python script.
> 
> Also consider that even for non-incremental backups, we want full
> backups made subsequently to not, in general, overwrite the previous
> full backup, so the TARGET is more of a "living entity" than a fixed
> thing, even in the simple case.

Patterns would be nice.  You may find string.Template() useful:
https://docs.python.org/2.7/library/string.html#template-strings
https://docs.python.org/3/library/string.html#template-strings

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