Planning for and enabling collocation

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Understanding the effects of collocation can help reduce the number of media mounts, make better use of space on sequential volumes, and improve the efficiency of server operations.

About this task

Table 1 lists the four collocation options that you can specify on the DEFINE STGPOOL and UPDATE STGPOOL commands. The table also shows the effects of collocation on data that belongs to nodes that are and are not members of collocation groups.
Table 1. Collocation options and the effects on node data
Collocation option If a node is not defined as a member of a collocation group If a node is defined as a member of a collocation group
No The data for the node is not collocated. The data for the node is not collocated.
Group The server stores the data for the node on as few volumes in the storage pool as possible. The server stores the data for the node and for other nodes that belong to the same collocation group on as few volumes as possible.
Node The server stores the data for the node on as few volumes as possible. The server stores the data for the node on as few volumes as possible.
File space The server stores the data for the node's file space on as few volumes as possible. If a node has multiple file spaces, the server stores the data for different file spaces on different volumes in the storage pool. The server stores the data for the node's file space on as few volumes as possible. If a node has multiple file spaces, the server stores the data for different file spaces on different volumes in the storage pool.
Table 2. Collocation group options and effects on file space data
Collocation option If a file space is not defined as a member of a collocation group If a file space is defined as a member of a collocation group
No The data for the file space is not collocated. The data for the file space is not collocated.
Group The server stores the data for the file space on as few volumes in the storage pool as possible. The server stores the data for the file space and other file spaces that belong to the same collocation group on as few volumes as possible.
Node The server stores the data for the node on as few volumes as possible. The server stores the data for the node on as few volumes as possible.
File space The server stores the data for the node's file space on as few volumes as possible. If a node has multiple file spaces, the server stores the data for different file spaces on different volumes in the storage pool. The server stores the data for the file spaces on as few volumes as possible. If a node has multiple file spaces, the server stores the data for different file spaces on different volumes in the storage pool.

Procedure

To determine whether and how to collocate data, complete the following steps:

  1. Determine how to organize data, whether by client node, group of client nodes, or file space. To collocate by group, you must decide how to group nodes:
    • If the goal is to save space, you might want to group small nodes together to better use tapes.
    • If the goal is potentially faster client restores, group nodes together so that they fill as many tapes as possible. By grouping nodes together, the individual node data is distributed across two or more tapes and that more tapes can be mounted simultaneously during a multi-session no-query restore operation.
    • If the goal is to departmentalize data, you can group nodes by department.
  2. To collocate groups, complete the following steps:
    1. Define collocation groups with the DEFINE COLLOCGROUP command.
    2. Add client nodes to the collocation groups with the DEFINE COLLOCMEMBER command.
    The following query commands are available to help in collocating groups:
    QUERY COLLOCGROUP
    Displays the collocation groups that are defined on the server.
    QUERY NODE
    Displays the collocation group, if any, to which a node belongs.
    QUERY NODEDATA
    Displays information about the data for one or more nodes in a sequential-access storage pool.
    QUERY STGPOOL
    Displays information about the location of client data in a sequential-access storage pool and the amount of space a node occupies in a volume.

    You can also use IBM Storage Protect server scripts or PerlL scripts to display information that can be useful in defining collocation groups.

  3. Specify how data must be collocated in a storage pool by issuing the DEFINE STGPOOL or UPDATE STGPOOL command and specifying the COLLOCATE parameter.

What to do next

Tip: To reduce the number of media mounts, use space on sequential volumes more efficiently, and enable collocation, complete the following steps:
  • Define a storage pool hierarchy and policy to require that backed-up, archived, or space-managed files are initially stored in disk storage pools.

    When files are migrated from a disk storage pool, the server attempts to migrate all files that belong to the client node or collocation group that is using the most disk space in the storage pool. This process works well with the collocation option because the server tries to place all of the files from a particular client on the same sequential-access storage volume.

  • Use scratch volumes for sequential-access storage pools to allow the server to select new volumes for collocation.
  • Specify the client option COLLOCATEBYFILESPEC to limit the number of tapes to which objects associated with one file specification are written. This collocation option makes collocation by the server more efficient; it does not override collocation by file space or collocation by node.