Sébastien Han

Stacker! Cepher! What's next?

Ceph and Cinder multi-backend

Grizzly brought the multi-backend functionality to cinder and tons of new drivers. The main purpose of this article is to demonstrate how we can take advantage of the tiering capability of Ceph.

I. Ceph

To configure Ceph to use different storage devices see my previous article: Ceph 2 speed storage with CRUSH.


II. Cinder

Assuming your 2 pools are called:

  • rbd-sata points to the SATA rack
  • rbd-ssd points to the SSD rack

II.1 Configuration

Cinder configuration file:

# Multi backend options

# Define the names of the groups for multiple volume backends
enabled_backends=rbd-sata,rbd-ssd

# Define the groups as above
[rbd-sata]
volume_driver=cinder.volume.driver.RBDDriver
rbd_pool=cinder-sata
volume_backend_name=RBD_SATA
# if cephX is enable
#rbd_user=cinder
#rbd_secret_uuid=<None>
[rbd-ssd]
volume_driver=cinder.volume.driver.RBDDriver
rbd_pool=cinder-ssd
volume_backend_name=RBD_SSD
# if cephX is enable
#rbd_user=cinder
#rbd_secret_uuid=<None>

Unfortunately the rbd driver doesn’t support this variable yet (most of the drivers don’t). This feature has been submitted here: https://review.openstack.org/#/c/28208/.

Then create the pointers:

$ cinder type-key ssd set volume_backend_name=RBD_SSD
$ cinder type-key sata set volume_backend_name=RBD_SATA
$ cinder extra-specs-list
+--------------------------------------+------+---------------------------------------+
| ID | Name | extra_specs |
+--------------------------------------+------+---------------------------------------+
| b1522968-e4fa-4372-8ac4-3925b7c79ee1 | ssd | {u'volume_backend_name': u'RBD_SSD'} |
| b50bf5a3-6044-4392-beeb-432302f6421c | sata | {u'volume_backend_name': u'RBD_SATA'} |
+--------------------------------------+------+---------------------------------------+

Then restart cinder services:

$ sudo restart cinder-api ; sudo restart cinder-scheduler ; sudo restart cinder-volume

Eventually create 2 volume type, one for each backend:

$ cinder type-create ssd
+--------------------------------------+------+
| ID | Name |
+--------------------------------------+------+
| b1522968-e4fa-4372-8ac4-3925b7c79ee1 | ssd |
+--------------------------------------+------+

$ cinder type-create sata
+--------------------------------------+------+
| ID | Name |
+--------------------------------------+------+
| b50bf5a3-6044-4392-beeb-432302f6421c | sata |
+--------------------------------------+------+


II.2. Play with it

$ cinder create --volume_type ssd --display_name vol-ssd 1
+---------------------+--------------------------------------+
| Property | Value |
+---------------------+--------------------------------------+
| attachments | [] |
| availability_zone | nova |
| bootable | false |
| created_at | 2013-04-22T14:54:53.917580 |
| display_description | None |
| display_name | vol-ssd |
| id | 4c777d96-66e4-4f85-815c-92d4503c5c8c |
| metadata | {} |
| size | 1 |
| snapshot_id | None |
| source_volid | None |
| status | creating |
| volume_type | ssd |
+---------------------+--------------------------------------+

$ cinder create --volume_type ssd --display_name vol-sata 1
+---------------------+--------------------------------------+
| Property | Value |
+---------------------+--------------------------------------+
| attachments | [] |
| availability_zone | nova |
| bootable | false |
| created_at | 2013-04-22T14:54:58.831327 |
| display_description | None |
| display_name | vol-sata |
| id | 8e347bd1-2044-40a2-ae87-ee9a23cddd71 |
| metadata | {} |
| size | 1 |
| snapshot_id | None |
| source_volid | None |
| status | creating |
| volume_type | ssd |
+---------------------+--------------------------------------+

Does it work?

$ rbd -p cinder-ssd ls
volume-8e347bd1-2044-40a2-ae87-ee9a23cddd71

$ rbd -p cinder-sata ls
volume-4c777d96-66e4-4f85-815c-92d4503c5c8c


It’s nice that the multi-backend came with Cinder, we are gradually getting to enjoy the full power of Ceph!

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