How Files Are Migrated

After you have specified migration policies for your migration client in the Migration resource, Backup migrates files in the following way:

1. When the Backup server conducts a regularly scheduled backup, it checks each client in the backup group for files that are candidates for migration. During a scheduled backup, the premigration command, nsrpmig, searches the migration client filesystem for files that meet the migration criteria.

   Premigration is a resource-intensive activity. The group containing migration clients should start its scheduled backup at a time of low system use.

2. Files that meet the migration criteria are premigrated. During premigration, the file is copied to a Backup storage location (a migration volume), but the original file remains on the client machine.

3. When the client filesystem reaches the high water mark, the nsrexecd daemon starts the migration command, nsrmig, and migration occurs automatically. The nsrmig command checks the premigrated files to ensure that they still meet the migration criteria. If the premigrated files are still candidates for migration, the nsrmig command does the following:

   • Renames the original file on the client filesystem with a temporary name.

   • Creates a stub file on the client filesystem to point to the migrated file on the migration media.

   • Deletes the original file from the client filesystem.

4. Migration continues until the low water mark is reached. If not enough files meet the migration criteria, the migration process might not meet the low water mark.

5. A migration report is emailed to the administrator.

   Backup makes entries for migrated files in the client index. These entries, however, are not visible to a user through the recovery GUI. Backup uses these entries to track the link between the migrated file and the stub file in the client filesystem as well as for recall purposes. Because a migrated file must be available for a user to recall, the index entries for migrated data are exempt from the automatic data recycling policies set for a Backup client. See "How HSM Handles Renamed or Deleted Files" for details on how Backup handles files that have been deleted from the client filesystem.