Improving read performance for deduplicated storage pools

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To obtain the different extents that make up a file from a deduplicated storage pool, client restore operations and certain server processes might require opening and closing FILE volumes multiple times. The frequency with which FILE volumes are opened and closed during a session can severely affect performance.

About this task

Opening and closing volumes multiple times can affect the following server processes that read data from a deduplicated storage pool:
  • Volume reclamation
  • MOVE DATA or MOVE NODEDATA
  • EXPORT
  • AUDIT VOLUME
  • Storage-pool restore operation
  • Volume restore operation
  • Data migration

To reduce the number of times a volume is opened and closed, IBM Storage Protect allows multiple input FILE volumes in a deduplicated storage pool to remain open at the same time during a session. To specify the number of open FILE volumes in deduplicated storage pools that can remain open, use the NUMOPENVOLSALLOWED server option. Set this option in the server options file or by using the SETOPT command.

During a client-restore operation, volumes can remain open for as long as the client session is active. During a no-query restore operation, the volumes remain open until the no-query restore completes. Then, all volumes are closed and released. However, for a standard restore operation started in interactive mode, the volumes might remain open at the end of the restore operation. The volumes are closed and released when the next classic restore operation is requested.

Procedure

This option can significantly increase the number of volumes and mount points in use at any one time. To optimize performance, complete the following tasks:
  • To set NUMOPENVOLSALLOWED:
    1. Select a beginning value. The default is 10. A small increase to this option can be beneficial but that might not be true in all environments.
    2. Monitor client sessions and server processes.
    3. Note the highest number of volumes open for a single session or process. If the highest number of open volumes is equal to the value specified by NUMOPENVOLSALLOWED, increase the setting of NUMOPENVOLSALLOWED.
  • To prevent sessions or processes from having to wait for a mount point:
    1. Increase the value of the MOUNTLIMIT parameter in the device-class definition.
    2. Set the value of the MOUNTLIMIT parameter high enough to allow all client sessions and server processes that are using deduplicated storage pools to open the number of volumes that are specified by the NUMOPENVOLSALLOWED option.
    3. Check the following results:
      • For client sessions, check the destination in the copy group definition to determine how many nodes are storing data in the deduplicated storage pool.
      • For server processes, check the number of processes that are allowed for each process for the storage pool.
  • For any node that is backing up or archiving data into a deduplicated storage pool, set the value of the MAXNUMMP parameter in the client-node definition to a value at least as high as the NUMOPENVOLSALLOWED option. Increase this value if you notice that the node is failing client operations because the MAXNUMMP value is being exceeded.

Results

Each session within a client operation or server process can have as many open FILE volumes as specified by this option. A session is initiated by a client operation or by a server process. Multiple sessions can be started within each.