The Tivoli® Storage Manager for Space Management client provides both automatic and selective migration. Once file migration begins, the Tivoli Storage Manager for Space Management client sends a copy of your file to storage volumes on disk devices or devices that support removable media, such as tape and replaces the original file with a stub file on your local file system.
The stub file is a small replacement file that makes it appear as though the original file is on the local file system. It contains required information to locate and recall a migrated file and to respond to specific UNIX commands without recalling the file.
Automatic migration monitors space usage and automatically migrates eligible files according to the options and settings that you select. The Tivoli Storage Manager for Space Management client provides two types of automatic migration: threshold migration and demand migration.
Threshold migration maintains a specific level of free space on your local file system. When space usage reaches the high threshold that you set for your file system, eligible files are migrated to storage automatically. When space usage drops to the low threshold that you set for your file system, file migration stops.
Demand migration responds to an out-of-space condition on your local file system. Demand migration starts automatically if your file system runs out of space. For HSM on AIX® JFS2, as files are migrated, space becomes available on your file system and the process or event that caused the out-of-space condition continues. On AIX GPFS™ and Linux x86_64 GPFS, the process receives an out-of-space (ENOSPC) return code and stops.
On GPFS file systems, you can use the GPFS policy engine to monitor space thresholds and search for migration candidates.
For information about configuring GPFS integration with the Tivoli Storage Manager for Space Management client, see the Tivoli field guide TSM for Space Management for UNIX-GPFS Integration Part I: Policy-driven Threshold Migration at https://www.ibm.com/support/docview.wss?uid=swg27018848.
Selective migration moves specific files from your local file system to storage. For example, if you know that you will not be using a particular group of files for an extended time, you can migrate them to storage to free additional space on your local file system.