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.
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.
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.
Files status can have several values in DMF:
REG: Regular files are user files residing only on disk
MIG: Migrating files are files which are being copied from disk to tape
UNM: Unmigrating files are files which are being copied from tape to disk
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 -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 * $ 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).