# The CSM plug-in

The Cluster Segment Manager (CSM) is the EVMS plug-in that identifies and manages cluster storage. The CSM protects disk storage objects by writing metadata at the start and end of the disk, which prevents other plug-ins from attempting to use the disk. Other plug-ins can look at the disk, but they cannot see their own metadata signatures and cannot consume the disk. The protection that CSM provides allows the CSM to discover cluster storage and present it in an appropriate fashion to the system.

All cluster storage disk objects must be placed in containers that have the following attributes:

- cluster ID that identifies the cluster management software

- node ID that identifies the owner of the disk objects

- storage type: private, shared, or deported

The CSM plug-in reads metadata and constructs containers that consume the disk object. Each disk provides a usable area, mapped as an EVMS data segment, but only if the disk is accessible to the node viewing the storage.

The CSM plug-in performs these operations:

- examines disk objects

- creates containers

- uses the containers to consume disk objects

- produces data segment objects if the disk is accessible to the node

## Assigning the CSM plug-in

Assigning a segment manager to a disk means that you want the plug-in to manage partitions on the disk. In order to do this, the plug-in needs to create and maintain appropriate metadata. The CSM creates the follow three segments on the disk:

- primary metadata segment

- usable area data segment

- secondary metadata segment

The CSM collects the information it needs to perform the assign operation with the following options:

NodeId

  Choose only from a list of configured node IDs that have been provided to the CSM by clustering software. The default selection is the node from which you are running the EVMS user interface.

Container Name

  The name for the container. You need to keep this name unique across the cluster to prevent name-in-conflict errors should the container fail over to another node that has a container with the same name.

Storage Type

  Can be either: share, private, or deported.

Note that you would typically assign the CSM to a disk when you want to add a disk to an existing CSM container. If you are creating a new container, you have a choice of using either: Actions CreateContainer or Actions AddSegment Manager.

If the container doesn't exist, it will be created for the disk. If the container already exists, the disk will be added to it.

## Unassigning the CSM plug-in

Unassigning a CSM plug-in results in the CSM removing its metadata from the specified disk storage object. The result is that the disk has no segments mapped and appears as a raw disk object. The disk is removed from the container that consumed it and the data segment is removed as well.

## Deleting a CSM container

An existing CSM container cannot be deleted if it is producing any data segments, because other EVMS plug-ins might be building higher-level objects on the CSM objects. To delete a CSM container, first remove disk objects from the container. When the last disk is removed, the container is also removed.