Difference between TSM storage pool and storage-pool volumes

In terms of Tivoli Storage Manager, tapes are referred as storage pool volumes (PRIVATE) if they are defined to any specific storage pool or volumes (SCRATCH) if they are not defined yet to any storage pool. In other words, the logical group of same types of tape volumes is known as Storage pool and volumes in the storage pool are referred as storage pool volumes. 

What is a Storage Pool ?

A storage pool is a collection of volumes that are associated with one device class and one media type. For example, a storage pool that is associated with a device class for LTO tape volumes contains only LTO tape volumes. You can control the characteristics of storage pools, such as whether scratch volumes are used. Tivoli Storage Manager supplies default disk storage pools.

For DISK device classes, you must define volumes. For other device classes, such as tape and FILE, you can allow the server to dynamically acquire scratch volumes and define those volumes as needed.

Also Read: TSM Storage Pool Concepts (V7 Revised)

One or more device classes are associated with one library, which can contain multiple drives. When you define a storage pool, you associate the pool with a device class. Volumes are associated with pools.
Ex :   define stgpool diskpool DISK maxsize=500m himig=90 lomig=60                                              pooltype=primary
          define stgpool copypool LTOTAPE pooltype=copy maxscr=100
          define stgpool activedatapool FILE pooltype=activedata maxscr=100

What are Storage Pool Volumes ?

A volume is the basic unit of storage for Tivoli Storage Manager storage pools. Tivoli Storage Manager volumes are classified according to status - private, scratch, and scratch write-once, read-many (WORM). Scratch WORM status applies to 349X libraries only when the volumes are IBM 3592 WORM volumes.
  • A Private volume is a labeled volume that is in use or owned by an application, and may contain valid data. You must define each private volume. Alternatively, for storage pools associated with sequential access disk (FILE) device classes, you can use space triggers to create private, preassigned volumes when predetermined space-utilization thresholds have been exceeded. Private FILE volumes are allocated as a whole. The result is less risk of severe fragmentation than with space dynamically acquired for scratch FILE volumes. A request to mount a private volume must include the name of that volume. Defined private volumes do not return to scratch when they become empty.
  • A Scratch volume is a labeled volume that is empty or contains no valid data and that can be used to satisfy any request to mount a scratch volume. When data is written to a scratch volume, its status is changed to private, and it is defined as part of the storage pool for which the mount request was made. When valid data is moved from the volume and the volume is reclaimed, the volume returns to scratch status and can be reused by any storage pool associated with the library.
  • A WORM scratch volume is similar to a conventional scratch volume. However, WORM volumes cannot be reclaimed by Tivoli Storage Manager reclamation processing. WORM volumes can be returned to scratch status only if they have empty space in which data can be written. Empty space is space that does not contain valid, expired or deleted data. (Deleted and expired data on WORM volumes cannot be overwritten.) If a WORM volume does not have any empty space in which data can be written (for example, if the volume is entirely full of deleted or expired data), the volume remains private.
Also Read: Points to remember when taking backup to multiple storagepools simultaneously

For each storage pool, you must decide whether to use scratch volumes. If you do not use scratch volumes, you must define private volumes, or you can use space-triggers if the volume is assigned to a storage pool with a FILE device type. Tivoli Storage Manager keeps an inventory of volumes in each automated library it manages and tracks whether the volumes are in scratch or private status. When a volume mount is requested, Tivoli Storage Manager selects a scratch volume only if scratch volumes are allowed in the storage pool. The server can choose any scratch volume that has been checked into the library.

You do not need to allocate volumes to different storage pools associated with the same automated library. Each storage pool associated with the library can dynamically acquire volumes from the library's inventory of scratch volumes. Even if only one storage pool is associated with a library, you do not need to explicitly define all the volumes for the storage pool. The server automatically adds volumes to and deletes volumes from the storage pool.

A disadvantage of using scratch volumes is that volume usage information, which you can use to determine when the media has reached its end of life, is deleted when a private volume is returned to the scratch volume pool.

What are Tape Library Volumes ?

A library's volume inventory includes only those volumes that have been checked into that library. This inventory is not necessarily identical to the list of volumes in the storage pools associated with the library. 

Also Read: Different types of libraries supported by IBM Spectrum Protect (TSM)
  • A volume can be checked into the library but not be in a storage pool (a scratch volume, a database backup volume, or a backup set volume).
  • A volume can be defined to a storage pool associated with the library (a private volume), but not checked into the library.
Ex :     Query Library TSMLIB
            Query Volume

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