Hi Satish,

Did you check the size of the actual backup file in ceph storage? It should be created in the backups pool[1].
Cinder shows the same size of incremental backup as a normal backup but file size should be different from
the size shown in cinder DB records. Also file size of incremental backup should not be the same as the file size of full backup.

[1] https://github.com/openstack/devstack/blob/34afa91fc9f830fc8e1fdc4d76e7aa6d4248eaaa/lib/cinder_backups/ceph#L22

Thanks
Rajat Dhasmana

On Wed, May 17, 2023 at 12:25 AM Satish Patel <satish.txt@gmail.com> wrote:
Folks,

I have ceph storage for my openstack and configure cinder-volume and cinder-backup service for my disaster solution. I am trying to use the cinder-backup incremental option to save storage space but somehow It doesn't work the way it should work. 

Whenever I take incremental backup it shows a similar size of original volume. Technically It should be smaller. Question is does ceph support incremental backup with cinder? 

I am running a Yoga release. 

$ openstack volume list
+--------------------------------------+------------+------------+------+-------------------------------------+
| ID                                   | Name       | Status     | Size | Attached to                         |
+--------------------------------------+------------+------------+------+-------------------------------------+
| 285a49a6-0e03-49e5-abf1-1c1efbfeb5f2 | spatel-vol | backing-up |   10 | Attached to spatel-foo on /dev/sdc  |
+--------------------------------------+------------+------------+------+-------------------------------------+

### Create full backup 
$ openstack volume backup create --name spatel-vol-backup spatel-vol --force
+-------+--------------------------------------+
| Field | Value                                |
+-------+--------------------------------------+
| id    | 4351d9d3-85fa-4cd5-b21d-619b3385aefc |
| name  | spatel-vol-backup                    |
+-------+--------------------------------------+

### Create incremental 
$ openstack volume backup create --name spatel-vol-backup-1 --incremental --force spatel-vol
+-------+--------------------------------------+
| Field | Value                                |
+-------+--------------------------------------+
| id    | 294b58af-771b-4a9f-bb7b-c37a4f84d678 |
| name  | spatel-vol-backup-1                  |
+-------+--------------------------------------+

$ openstack volume backup list
+--------------------------------------+---------------------+-------------+-----------+------+
| ID                                   | Name                | Description | Status    | Size |
+--------------------------------------+---------------------+-------------+-----------+------+
| 294b58af-771b-4a9f-bb7b-c37a4f84d678 | spatel-vol-backup-1 | None        | available |   10 |
| 4351d9d3-85fa-4cd5-b21d-619b3385aefc | spatel-vol-backup   | None        | available |   10 |
+--------------------------------------+---------------------+-------------+-----------+------+

My incremental backup still shows 10G size which should be lower compared to the first backup.