CA Dynam for VSE User Guide

Basic Components
Disk Space Availability
CA Dynam/D allocates disk space for files at OPEN time by searching the
specified disk volumes for available contiguous space. CA Dynam/D considers
disk space to be available on a volume when one of the following conditions
prevails:
• Disk space is unused
• Disk space is occupied by a file whose expiration date is less than the
current date
Files with an expiration date equal to the current date (0 retention days) are
considered unexpired by CA Dynam/D. The disk space occupied by these files
will not be released by CA Dynam/D until the following day (after midnight of
the day when the file was created).
Note: For FBA allocations, CA Dynam/D rounds all user allocation requests up
to an even multiple of 8 physical blocks for optimum performance. If, for
example, 7 blocks are requested either through JCL or the Catalog, 8 blocks
are allocated by CA Dynam/D.
Secondary Disk Space
Secondary disk space allocation lets you automatically acquire disk space
during program execution whenever the original EXTENT of a sequential disk
(SD) file is filled. This eliminates the problem of allocating a single large,
contiguous area of disk space big enough for a maximal amount of data.
This capability is important for files which vary in size from one job execution
to another. The allocated disk space can grow according to the file size.
You can define secondary space for a file in several ways. Firstly, you can use
Automatic Secondary Allocation. In this way, you define only the size of the
primary allocation. If secondary allocations are required, they are generated
based upon constants defined to the system using the DYNAM/D option record.
Secondly, for complete control over all the allocations permitted for a file, on a
file-by-file basis, define the following:
• Size of the primary allocation
• Size of the secondary allocation to be used if needed
• Number of desired secondary allocations
These definitions can be specified either with EXTENT statements, or in the
Catalog entry. To use each of the methods, see the examples that follow.
4–4 User Guide