Hi,

Cinder backup service discards excess bytes when restoring based on 
configuration.
https://github.com/openstack/cinder/blob/master/cinder/backup/drivers/ceph.py#L317
https://github.com/openstack/cinder/blob/master/cinder/backup/drivers/ceph.py#L284


Lisa

From: 刘庆 [mailto:win...@gmail.com]
Sent: Friday, June 24, 2016 11:05 AM
To: openstack-dev@lists.openstack.org
Subject: [openstack-dev] [cinder]restore method while ceph backup backend is 
used

Hi all,
This is Liu Qing, new to this community. I have a question about the ceph 
backup backend.
From the cinder/backup/manager.py, the restore process is done by attach the 
original device(restore dest) to the cinder service host. And in the ceph 
driver the full_restore will discard the additional space if restore dest(by 
volume extend) is larger than the backup. There are two ways to discard the 
unused space, by ceph discard or write zeroes to the unused space. As the dest 
is attached to the host, the dest is not recognized as an ceph volume. Ceph 
discard will never be used in volume restore, right? But ceph discard is much 
more efficient than writing zeroes to the unused space. Is there any plan to 
use the ceph discard way? Thanks.

Liu Qing
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