CA Dynam for VSE User Guide

Controlling Disk Pools
In order to use the Disk Pool Management facility, the following conditions
must be satisfied:
• COMPOOL option record must be defined. For more information about
using the COMPOOL option record, see the Programming Guide.
• Data file must be under the control of CA Dynam/D (relative track equal to
the CA Dynam/D trigger value or defined in the Catalog).
Rotating Disk Pool Volumes
Rotation of disk pool volumes is a vital feature of disk pool management. In
order to achieve well-balanced disk volume usage, CA Dynam/D will optionally
use the volumes defined in the disk pool on an equal basis. When this option,
ROTATE(YES), is in use, CA Dynam/D remembers the last volume used and
searches for the next volume in the pool when attempting a subsequent space
allocation.
This rotation of disk volume usage ensures that data files are spread across
several volumes defined in the pool, thereby creating an environment of
optimum file-accessing efficiency.
When using pool rotation, CA Dynam/D begins searching for free space
starting at the volume which follows the one last used. If the previous open
began its search at the last volume in the pool, the next starting point is at the
first volume defined.
The rotation of starting volumes is performed regardless of the partition
issuing the open request. As mentioned, the rotation only affects the starting
point for the free space search.
If the starting volume does not contain the required amount of available
space, or is not mounted, the search continues to the next volume. Full
wraparound from the last volume defined in the pool to the first volume is
supported.
The only exception to pool rotation is the secondary allocation of sequential
disk files. If the open is for a secondary extent, CA Dynam/D attempts to start
the free space search on the volume containing the primary extent for the file.
This avoids exhausting all available volumes with secondary extents.
Chapter 4: Disk File Management 4–31