[openstack-dev] [nova] Two questions about 'backup' API

wu jiang wingwj at gmail.com
Thu Jun 26 12:07:55 UTC 2014

Hi all,

I tested the 'backup' API recently and got two questions about it:

1. Why 'daily' & 'weekly' appear in code comments & novaclient about
'backup_type' parameter?

The 'backup_type' parameter is only a tag for this backup(image).
And there isn't corresponding validation for 'backup_type' about these two

Moreover, there is also no periodic_task for 'backup' in compute host.
(It's fair to leave the choice to other third-parts system)

So, why we leave 'daily | weekly' example in code comments and novaclient?
IMO it may lead confusion that Nova will do more actions for 'daily|weekly'
backup request.

2. Is it necessary to backup instance when 'rotation' is equal to 0?

Let's look at related codes in nova/compute/manager.py:
#     def backup_instance(self, context, image_id, instance, backup_type,
#        self._do_snapshot_instance(context, image_id, instance, rotation)
#        self._rotate_backups(context, instance, backup_type, rotation)

I knew Nova will delete all backup images according the 'backup_type'
parameter when 'rotation' equals to 0.

But according the logic above, Nova will generate one new backup in
_do_snapshot_instance(), and delete it in _rotate_backups()..

It's weird to snapshot a useless backup firstly IMO.
We need to add one new branch here: if 'rotation' is equal to 0, no need to
backup, just rotate it.

So, what's your opinions? Look forward to your suggestion.

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