5.3 IBM Tivoli Storage Manager Collocation Overview


What is TSM Collocation ?

Collocation is the process by which the server minimizes the number of sequential access storage volumes to keep files of a single client node or file space of a client node. You can set collocation for each sequential access storage pool when you define or update the pool.

TSM Collocation Overview
Image Source: IBM

By using collocation, you reduce the number of volume mount operations, and the amount of time searching database entries when users restore, retrieve, or recall multiple files. Thus, collocation improves access time for these operations. If collocation is enabled and reclamation occurs, the server tries to reclaim the files for each client node or client file space onto a minimal number of volumes. Collocation cannot collocate data that is already in a storage pool volume. The following options are available for collocation when you use the define stgpool or update stgpool commands
  • No
  • Node
  • File space
  • Group by node
  • Group by file space

Collocation of active data
You can also collocate active data to active-data pools by using one of the following methods
  • Writing data to multiple pools by using simultaneous write. 
  • Copying data to an active-data pool by using the COPY ACTIVEDATA command. Only active versions of backup data are copied from a primary storage pool to an active-data pool. You use the following command
   copy activedata primary_pool_name activedata_pool_name

How collocation process select volumes ?

Setting COLLOCATION=NODE causes Tivoli Storage Manager to try to put data for one node on as few volumes as possible.

Setting COLLOCATION=FILESPACE causes Tivoli Storage Manager to try to put data for file space for one client node on as few volumes as possible.

Volume selection criteria for COLLOCATION=NODE
  •  A volume that contains files from the same client node.
  • An empty, predefined volume.
  • An empty, scratch volume.
  • Among volumes that contain data, the one with the most free space.
Volume selection criteria for COLLOCATION=FILESPACE
  • A volume that contains files from the same file space of that client node.
  • An empty, predefined volume.
  • An empty, scratch volume.
  • A volume that contains data from the same client node.
  • Among volumes that contain data, the one with the most free space.
Collocation by groups of nodes

Collocation by group provides the following benefits. You must update the storage pool to use collocation by group.
  • Reduce unused tape capacity, with more collocated data on individual tapes.
  • Minimize mounts of target volumes.
  • Minimize database scanning and reduce tape passes for sequential-to-sequential transfer.
  • Minimize database scanning, which reduces tape passes for sequential-to-sequential transfers, such as reclamation.
Also Read: Tips to fix the TSM server startup problems

Use the define collocgroup command to define the group of nodes or filespaces for collocation
define collocgroup groupname

Use the define collocmember command to add a client node to a collocation group
define collocmember groupname node1,node2

After you define groups of nodes, the server can collocate data according to these groups.

Collocation by groups of file spaces

Similarly, use the define collocgroup command to define the group of nodes or filespaces for collocation
define collocgroup groupname

Use the define collocmember command to add a client node to a collocation group
define collocmember groupname filespace1,filespace2





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