CA Dynam for VSE User Guide

Defining Minimum Space Allocation
The serial number SYS*** causes CA Dynam/D to search the disks for the first
occurrence of a VOLID beginning with the characters SYS. The first disk found
with 38 contiguous tracks available was SYSWK1 at address 205. Note that the
space was allocated starting at relative track 153. A temporary assignment
was then made for logical unit SYS008 to device address 205.
Defining Minimum Space Allocation
The minimum percentage allocation value is used to define the minimum value
CA Dynam/D will accept in allocating disk space. Your data center defines this
value at CA Dynam/D installation time (ARFACTR).
This facility offers you great flexibility in allocating disk space because CA
Dynam/D will adapt its space allocation algorithm to the particular disk volume
it is processing. Thus, programmers' jobs are much less likely to be
interrupted because of insufficient disk space.
With minimum percentage space allocation defined, CA Dynam/D searches the
VTOC once only for available disk space; no additional overhead is incurred.
CA Dynam/D will always attempt to initially allocate the requested number of
tracks. If this allocation request cannot be satisfied, then CA Dynam/D
continues to search for available disk space. This is accomplished by allocating
the largest contiguous free space available that is greater than the minimum
percentage defined in the DYNAM/D option record.
In order to illustrate the processing logic of CA Dynam/D minimum percentage
allocation, consider the following example. Assume that the minimum
percentage value is 95%.
// USER'S JOB CONTROL FOR THE FILE
// DLBL FILEA,'DISK.FILE'
// EXTENT SYS008,999999,1,0,1,100
At OPEN, CA Dynam/D initially attempts to allocate 100 tracks on disk volume
999999. If there is not sufficient disk space available, CA Dynam/D searches
for the largest contiguous space which is available. From the example above, if
the largest available space is found to contain more than 95 contiguous tracks
(96—100 tracks), CA Dynam/D automatically allocates the necessary disk
space, and processing continues.
Otherwise, CA Dynam/D begins its RECOVERY process, because the minimum
percentage value of 95% has not been reached.
Chapter 4: Disk File Management 4–35