DMF (Data Migration Facility)

DMF (Data Migration Facility) is a hierarchical storage management system for Silicon Graphics environments. Its primary purpose is to augment the economic value of storage media and stored data.

How DMF works

Disk space capacity is handled by selecting which file systems DMF will manage and by specifying the volume of free space that will be maintained on each files system. Space management begins with a list of user files that are ranked according to file size and file age.

File migration occurs in two stages. First, a file is migrated to an offline medium. Once the offline copy is secure, the file is eligible to have its data blocks released (this usually occurs after a minimum space threshold is reached). A file with all offline copies completed is called fully backed up. A file that is fully backed up but whose data blocks have not been released, is called a dual-state file; its data exists both online and offline, simultaneously. After a file's data blocks have been released, the file is called an offline file.

Migrated files remain cataloged in their original directories and are accessed as if they were still on disk. The only difference users might notice is a delay in access time.

User commands

On Huygens, commands are provided for file owners to affect the manual storing and retrieval of data. Users can do the following:

  • dmput: Explicitly migrate files
  • dmget: Explicitly recall files or parts of files
  • dmcopy: Copy all or part of the data from a migrated file to an online file
  • dmls: Determine whether a file is migrated
  • dmattr: Test in shell scripts whether a file is online or offline
  • dmfind: Search for migrated files

See the online manual pages for details.

DMF file types

DMF regards files as being one of the following:

  • REG: Regular files are user files residing only on disk
  • MIG: Migrating files are files whose offline copies are in progress
  • UNM: Unmigrating files are files whose online copies are in progress
  • Migrated files can be either of the following:
    • DUL: Dual-state files whose data resides both online and offline
    • OFL: Offline files whose data is no longer on disk

Example of the "dmls" command:

$ dmls -l
-rw-------    1 hthta    staff     632792 Jul 26  1999 (OFL) file1
-rw-------    1 hthta    staff     632792 Jul 27  1999 (OFL) file2
-rw-------    1 hthta    staff      15884 Jul 27  1999 (REG) file3
-rw-------    1 hthta    staff     632792 Aug  2  1999 (DUL) file4
-rw-------    1 hthta    staff     632792 Jun 19 23:20 (MIG) file5

Example of the "dmget" command:

$ dmget *
$ dmls -l
-rw-------    1 hthta    staff     632792 Jul 26  1999 (DUL) file1
-rw-------    1 hthta    staff     632792 Jul 27  1999 (DUL) file2
-rw-------    1 hthta    staff      15884 Jul 27  1999 (REG) file3
-rw-------    1 hthta    staff     632792 Aug  2  1999 (DUL) file4
-rw-------    1 hthta    staff     632792 Jun 19 23:20 (MIG) file5

All the files with (OFL) changed their status to (DUL).