CA Dynam for VSE User Guide

Direct Access File Independence Facility (VCKD)
FBA Disk Files
Mapping FBA Disk Files
VCKD provides two data-mapping techniques for Direct Access files: full-track
mapping and record mapping.
• Full-track mapping combines all the key and data records from the original
CKD track into one control interval. All I/O to the file is then performed at
the track level. If the file contains physical keys, track mapping must be
specified.
• Record mapping creates a separate control interval for each data record on
the original CKD track. I/O for the file is then performed at the record
level. Record mapping provides faster access to records and reduced
storage requirements. However, it is supported only for fixed-length
records.
Specify the mapping technique as a parameter within the file name of a DLBL
JCL statement. This parameter has the following format:
MAP=T
MAP=R
- for track mapping
- record mapping
If MAP= is not specified, the default is full-track mapping. A file that has been
created for record mapping cannot be accessed as track-mapped.
Examples
Indicates record mapping.
// DLBL FBAFILE,'NEW.FBA.FILE.MAP=R',,DA Indicates track mapping, by default.
// DLBL FBAFILE,'NEW.FBA.FILE',,DA
Allocating FBA Disk Files
There are two methods of determining the number of FBA blocks to allocate
for the new FBA DA file: direct calculation, and VCKD Disk Analyzer Program
(VCKDANAL) use.
• Direct Calculation
VCKD emulates each CKD track as "n" FBA blocks. The actual number of
FBA blocks that make up each CKD track is based upon the CKD device
type, key and data lengths, and the number of records per track.
6–46 User Guide