Tivoli Storage Manager policies govern the following client operations, which are discussed in this section:
Backup-archive clients can back up and restore files and directories. Backup-archive clients on UNIX systems can also back up and restore logical volumes. Backups allow users to preserve different versions of files as they change.
To guard against the loss of information, the backup-archive client can copy files, subdirectories, and directories to media controlled by the server. Backups can be controlled by administrator-defined policies and schedules, or users can request backups of their own data. The backup-archive client provides two types of backup:
The latest level of the UNIX backup-archive clients can also back up logical volumes. The logical volume must meet some of the policy requirements that are defined in the backup copy group. See Using the Backup-Archive Client for details of this function.
When a user restores a backup version of a file, the server sends a copy of the file to the client node. The backup version remains in server storage. Restoring a logical volume backup works the same way.
If more than one backup version exists, a user can restore the active backup version or any inactive backup versions.
If policy is properly set up, a user can restore backed-up files to a specific time. See Defining and Updating a Backup Copy Group for details on the requirements.
To preserve files for later use or for records retention, a user with a backup-archive client can archive files, subdirectories, and directories on media controlled by the server. When users archive files, they can choose to have the backup-archive client erase the original files from their workstation after the client archives the files.
When a user retrieves a file, the server sends a copy of the file to the client node. The archived file remains in server storage.
When the Tivoli Space Manager product is on the workstation, a user can migrate files from workstation storage to server storage and recall those files as needed. Tivoli Space Manager frees space for new data and makes more efficient use of your storage resources. The installed Tivoli Space Manager product is also called the space manager client or the HSM client.
Files that are migrated and recalled with the HSM client are called space-managed files.
For details about using Tivoli Space Manager, see Using the UNIX HSM Clients.
When a file is migrated to the server, it is replaced on the client node with a small stub file of the same name as the original file. The stub file contains data needed to locate the migrated file on server storage.
Tivoli Space Manager provides selective and automatic migration. Selective migration lets users migrate files by name. The two types of automatic migration are:
To prepare for efficient automatic migration, Tivoli Space Manager copies a percentage of user files from the client node to the Tivoli Storage Manager server. The premigration process occurs whenever Tivoli Space Manager completes an automatic migration. The next time free space is needed at the client node, the files that have been premigrated to the server can quickly be changed to stub files on the client. The default premigration percentage is the difference between the high and low thresholds.
Files are selected for automatic migration and premigration based on the number of days since the file was last accessed and also on other factors set at the client node.
Tivoli Space Manager provides selective and transparent recall. Selective recall lets users recall files by name. Transparent recall occurs automatically when a user accesses a migrated file.
Migration and premigration can create inconsistencies between stub files on the client node and space-managed files in server storage. For example, if a user deletes a migrated file from the client node, the copy remains at the server. At regular intervals set at the client node, TSM compares client node and server storage and reconciles the two by deleting from the server any outdated files or files that do not exist at the client node.