IBM Support

Concurrent Migration Processes and Constraints

Question & Answer


Question

How to increase the number of concurrent migration processes and why there are only "n" number of concurrent migration processes initiated.

Cause

Often times there is confusion when it comes to the number of concurrent migration processes which initiate during migration

Answer

To increase the maximum number of migration processes allowed when migration starts - update the MIGPRocess option within the storage pool, this can be done during the DEFINE STGPOOL or UPDATE STGPOOL commands.

However, regardless of what the MIGPRocess parameter is set to, there is a limit on the number of migration processes which actually initiate depending on the environment:

1. Migration is first constrained by the number of client nodes which have data stored in the storage pool.
The Tivoli Storage Manager organizes client data by type, followed by node name, and then by filespace name. The server determines the cumulation of client node data (sorted by type, node, and filespace) consuming the most space in this storage pool. One migration thread will be started per node, moving the data for the largest filespace first (followed by the other filespaces for this same node). There is an exception when migrating data from sequential FILE storage pool, which is constrained based on the number of volumes instead of the number of nodes within the storage pool.

    example: A storage pool contains data from 3 nodes, when migration begins and MIGPRocess is set to 5, the maximum number of migration processes which can initiate is 3. (limited by the number of nodes)
2. If migrating from disk to tape drives - the maximum number of migration processes is further constrained by the amount of tape drives and tapes available.
    example: Assume there is a DISK class storage pool which contains data from 10 nodes and the MIGPRocess parameter set to '10'. In this case data is being migrated to a TAPE class storage pool with a library that only has 4 drives and 6 tapes available, a maximum of 4 concurrent migration processes can be initiated. (limited by the number of tape drives within the library).
    note: If a tape drive is in use when migration is initiated, the number of processes is further restrained

3. If migrating from a sequential FILE storage pool to another storage pool, the number of nodes within the storage pool will not constrain the number of migration processes, instead this type of storage pool is constrained by the number of volumes within.
    example: Assume there is a FILE storage pool with a single node and 5 volumes in it. Migprocess is set to 2. When migrating from FILE pool to TAPE pool, there will be 2 separate migration process started.

As referenced on page 311 of the v6.3 Tivoli Storage Manager Admin Guide (SC23-9773-04):

"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."

In conclusion the storage pool's MIGPRocess parameter, stored node data, and available tape mounts all constrain the amount of concurrent migration processes which initiate.

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Product Synonym

TSM

Document Information

Modified date:
17 June 2018

UID

swg21633725