Backup and restore on space managed file systems

Coordinate backup and migration to protect the file system data.

When you back up a file with the backup-archive client, a copy of the file is created on the Tivoli® Storage Manager server. The original file remains in your local file system. To obtain a backed file from Tivoli Storage Manager server storage, for example in case the file is accidentally deleted from the local file system, you restore the file. In contrast, when you archive a file to Tivoli Storage Manager server storage, that file is removed from your local file system, and if needed, you retrieve it from Tivoli Storage Manager storage.

When you migrate a file, you move the file to Tivoli Storage Manager server storage and replace it with a stub file on your local file system. You can then use that stub file to recall the full file from its migration location.

Regularly use a Tivoli Storage Manager backup-archive client to guard against loss or corruption of your data, regardless of whether the files are resident, migrated, or premigrated.

You can back up and migrate your files to the same Tivoli Storage Manager server or to different Tivoli Storage Manager servers. If you back up and migrate files to the same server, the HSM client can verify that current backup versions of your files exist before you migrate them. For this purpose, the same server stanza for backup and migration must be used. For example, if you are using the defaultserver and migrateserver options, they must both point to the same server stanza within the dsm.sys file. You cannot point to different server stanzas, even if they are pointing to the same Tivoli Storage Manager server.

To restore stub files rather than backup versions of your files, use the backup-archive client restore command with the restoremigstate option. To restore the stubs of space-managed files with the backup-archive client, the dsmrecalld daemon must be running. Your migrated and premigrated files remain intact on the Tivoli Storage Manager server, and you restore only the stub files on your local system. You cannot use the backup-archive client to restore stub files for your migrated files, if the files were backed up before the files were migrated. In this case, use the Tivoli Storage Manager for Space Management client dsmmigundelete command to re-create stub files for any migrated or premigrated files that are lost.

If you back up and migrate data to tape volumes in the same library, ensure that there are always some tape drives available for space management. You can limit the number of tape drives that can be used simultaneously by backup and archive operations. Specify a number for the mountlimit that is less than the total number of drives available in the library. Using disk storage as your primary storage pool for space management might, depending on the average size of your files, results in better performance than using tape storage pools.