Tuning the storage management cycle

The storage management cycle moves objects between disk, optical, and tape media, writes backup copies of objects, deletes expired objects, and expires optical cartridges when all the optical cartridge expiration criteria have been set. It should be run when the application work load is at a minimum.

You can obtain the shortest storage management cycle by making the best use of the library drives or operator-accessible drives in your SMS configuration. Your intent should be to process as many Object or Object Backup storage groups concurrently and use as many drives concurrently as possible without introducing contention for drives by different storage groups (which causes unnecessary mounts and demounts of cartridges).

OAM provides the following controls for tuning the storage management cycle:

The DRIVE STARTUP threshold attribute of each Object storage group definition and each Object Backup storage group definition determines the number of optical drives that are used concurrently for that storage group.
The TAPEDRIVESTARTUP threshold optional subparameter of the STORAGEGROUP parameter on the SETOAM statement, determines when OAM is to start additional tape drives for writing object data to tape volumes that belong to the Object and Object Backup storage groups. Consider the MAXTAPESTORETASKS keyword (for the OAM global level) and SGMAXTAPESTORETASKS keyword ( for the storage group level) with TAPEDRIVESTARTUP threshold for further controls within the storage management cycle..
Restriction: Do not specify a number greater than the number of tape drives available to OAM for the combined MAXTAPESTORETASKS, MAXTAPERETRIEVETASKS, SGMAXTAPESTORETASKS, and SGMAXTAPERETRIEVETASKS subparameters. This specification can cause a system to go into allocation recovery and attempt to allocate tape drives after all tape drives are in use causing system problems.
The CYCLE START TIME and CYCLE END TIME attributes of each Object or Object Backup storage group control the window in which the storage management cycle begins processing and (optionally, stops processing) the storage group.
The MAXS parameter of the OAM cataloged procedure controls the number of storage groups that the storage management cycle processes concurrently.
The UPD=N option on the OAM1 statement in IEFSSNxx member of PARMLIB reduces unnecessary retrieval and update of objects' directory entries during the OSMC cycle if your installation’s management classes do not use the TIME SINCE LAST USE or EXPIRE AFTER DAYS USAGE parameters.
In an OAMplex, the OSMC processing system name for each Object or Object Backup storage group controls where OSMC processing is done for that storage group. Using this parameter and separating hardware between storage groups can balance workload across systems for OSMC processing. Localize hardware and highest usage to reduce XCF overhead.

If your processing includes making object backups on operator-accessible optical disk drives, run as many Object storage groups concurrently as there are usable operator-accessible optical drives. If backup copies are not being made, you might be able to run as many Object storage groups concurrently as there are usable library drives in the configuration. Remember that in determining the number of Object storage groups to run concurrently, there are DB2 limitations which must be taken into account. See Tuning OAM connections to DB2 for additional information on these DB2 limitations.

Remember that OSMC functions other than the storage management cycle you start (for example, Volume Recovery utility, Move Volume utility, and others) are consumers of resources as well and need to be considered in your usage of the MAXS and DRIVE STARTUP threshold controls.

To avoid contention for drives within any one library, analyze the windows for processing each Object storage group. For example, if volumes for eight storage groups all reside in the same single optical library with four drives and MAXS=10, then the windows for the groups should be set so that no more than four overlap at any given time.

Recommendation: Consider all OAMs within an OAMplex when making decisions that affect those resources.

Attention: If you plan on using the CBRHADUX installation exit that is shipped with the SAMPLIB or plan on editing or creating your own CBRHADUX installation exit that does not allow expiration of objects, using this exit can cause OSMC performance problems if you have not properly established your expiration criteria in your SMS management classes.

If you do not plan on expiring objects and have established your CBRHADUX installation exit to return with an indication that no expiration is allowed, you must make sure that your SMS management class has expiration criteria that does not cause OSMC to continually pick objects to be expired. Always be sure that your management class sets the expiration criteria to NEVER expire if you do not plan to expire OAM objects.