File premigration

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For faster migration, the space management client prepares files for automatic migration by using a process that is called premigration.

Premigrated files are copied to IBM Storage® Protect server storage while the original files remain on your local file system. The next time that you need free space on your local file system, the space management client just changes the status of premigrated files to migrated files. No additional time is required to copy the files to storage.

The space management client verifies that files did not change since they became premigrated. When your premigrated files migrate to IBM Storage Protect server storage, stub files replace them on your local system.

The space management client premigrates files each time it completes automatic migration if the following conditions are true:
  • The file system contains extra files that are eligible for automatic migration.
  • The premigration percentage that you set for your file system is not reached or exceeded.
Note: For IBM® Storage Scale - Scale Out Backup and Restore (SOBAR) functionality, it is required that all files (including files with a size of zero bytes) are premigrated.

For example, if the high threshold is 90 percent and the low threshold is 80 percent, the premigration target default value is 10 percent. When space usage reaches the high threshold, files are migrated until space usage is 80 percent of the file system total space. Next, files are premigrated until at least 10 percent of the occupied space on your file system contains premigrated files. The next time that threshold migration is required, the space management client replaces the premigrated files with stub files. Space usage is quickly reduced to the low threshold. No files must be copied to IBM Storage Protect server storage.