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This patch adds info regarding the __DEFAULT__ type. Also how it can be removed and who should remove it. Change-Id: I21191218720aeca22a1aefabe5171718b4d39b41
3.5 KiB
Cinder Block Storage service overview
The OpenStack Block Storage service (Cinder) adds persistent storage to a virtual machine. Block Storage provides an infrastructure for managing volumes, and interacts with OpenStack Compute to provide volumes for instances. The service also enables management of volume snapshots, and volume types.
The Block Storage service consists of the following components:
- cinder-api
-
Accepts API requests, and routes them to the
cinder-volume
for action. - cinder-volume
-
Interacts directly with the Block Storage service, and processes such as the
cinder-scheduler
. It also interacts with these processes through a message queue. Thecinder-volume
service responds to read and write requests sent to the Block Storage service to maintain state. It can interact with a variety of storage providers through a driver architecture. - cinder-scheduler daemon
-
Selects the optimal storage provider node on which to create the volume. A similar component to the
nova-scheduler
. - cinder-backup daemon
-
The
cinder-backup
service provides backing up volumes of any type to a backup storage provider. Like thecinder-volume
service, it can interact with a variety of storage providers through a driver architecture. - Messaging queue
-
Routes information between the Block Storage processes.
The default volume type
Since the Train release, it is required that each volume must have a
volume type, and thus the required configuration option
default_volume_type
must have a value. A system-defined
volume type named __DEFAULT__
is created in the database
during installation and is the default value of the
default_volume_type
configuration option.
You (or your deployment tool) may wish to have a different volume type that is more suitable for your particular installation as the default type. This can be accomplished by creating the volume type you want using the Block Storage API, and then setting that volume type as the value for the configuration option. (The latter operation, of course, cannot be done via the Block Storage API.)
The system defined __DEFAULT__
volume type is a regular
volume type that may be updated or deleted. There is nothing special
about it. It only exists because there must always be at least one
volume type in a cinder deployment, and before the Block Storage API
comes up, there is no way for there to be a volume type unless the
system creates it.
Given that since the Victoria release it is possible to set a default
volume type for any project, having a volume type named
__DEFAULT__
in your deployment may be confusing to your
users, leading them to think this is the type that will be assigned
while creating volumes (if the user doesn't specify one) or them
specifically requesting __DEFAULT__
when creating a volume
instead of the actual configured default type for the system or their
project.
If you don't wish to use the __DEFAULT__
type, you may
delete it. The Block Storage API will prevent deletion under these
circumstances:
- If
__DEFAULT__
is the value of thedefault_volume_type
configuration option then it cannot be deleted. The solution is to make a different volume type the value of that configuration option. - If there are volumes in the deployment of the
__DEFAULT__
type, then it cannot be deleted. The solution is to retype those volumes to some other appropriate volume type.