Running multiple migration processes concurrently lets you make better use of your available tape drives or FILE volumes. When calculating the number of concurrent processes to run, you must carefully consider available resources.
Each migration process requires at least two simultaneous volume mounts (at least two mount points) and, if the device type is not FILE, at least two drives. One of the drives is for the input volume in the storage pool from which files are being migrated. The other drive is for the output volume in the storage pool to which files are being migrated.
When calculating the number of concurrent processes to run, carefully consider the resources you have available, including the number of storage pools that will be involved with the migration, the number of mount points, the number of drives that can be dedicated to the operation, and (if appropriate) the number of mount operators available to manage migration requests. The number of available mount points and drives depends on other Tivoli® Storage Manager and system activity and on the mount limits of the device classes for the storage pools that are involved in the migration.
For example, suppose that you want to migrate data on volumes in two sequential storage pools simultaneously and that all storage pools involved have the same device class. Each process requires two mount points and, if the device type is not FILE, two drives. To run four migration processes simultaneously (two for each storage pool), you need a total of at least eight mount points and eight drives if the device type is not FILE. The device class must have a mount limit of at least eight.
If the number of migration processes you specify is more than the number of available mount points or drives, the processes that do not obtain mount points or drives will wait indefinitely or until the other migration processes complete and mount points or drives become available.
To specify one or more migration processes for each primary sequential-access storage pool, use the MIGPROCESS parameter on the DEFINE STGPOOL and UPDATE STGPOOL commands.
The Tivoli Storage Manager server starts the specified number of migration processes regardless of the number of volumes that are eligible for migration. For example, if you specify ten migration processes and only six volumes are eligible for migration, the server will start ten processes and four of them will complete without processing a volume.
Multiple concurrent migration processing does not affect collocation. If you specify collocation and multiple concurrent processes, the Tivoli Storage Manager server attempts to migrate the files for each collocation group, client node, or client file space onto as few volumes as possible. If files are collocated by group, each process can migrate only one group at a single time. In addition, if files that belong to a single collocation group (or node or file space) are on different volumes and are being migrated at the same time by different processes, the files could be migrated to separate output volumes.
If simultaneous-write operations during migration are enabled during multiple concurrent-migration processing, each process has the following requirements: