ICBUF
The ICBUF keyword is optional on the GLBL and GROUP commands.
It is required on the IC and AIC commands if it is not specified on the GLBL or GROUP command. This keyword is available in ICPSYSIN; it is not available as a global option. The following table describes the keyword.
Table 1. Output image copy buffer algorithm keyword
To do this | Specify this in ICPSYSSIN |
|---|---|
Specify the output image copy buffer option. | ICBUF(value) |
Internal default: ICBUF(4) | |
Specify one of the following values to control the number of buffers that the Image Copy function allocates for each output image copy data set:
Table 2. ICBUF values
Value | Description |
|---|---|
0 | Tape or Disk: Use the MVS default or, if specified, the number of buffers on the DCB=BUFNO= parameter in the JCL input. |
1 | Tape: Use four buffers for SAM or EXCP. Disk: Use the number of buffers equal to one track of DASD space plus one buffer. |
2 | Tape: Use five buffers for SAM or eight buffers for EXCP. Disk: Use the number of buffers equal to two tracks of DASD space plus one buffer. |
3 | Tape: Use 9 buffers for SAM or 16 buffers for EXCP. Disk: Use the number of buffers equal to four tracks of DASD space plus one buffer. |
4 | Tape: Use 17 buffers for SAM or 32 buffers for EXCP. Disk: Use the number of buffers equal to one cylinder of DASD space plus one buffer. |
The Image Copy function allocates a minimum of 4 and a maximum of 255 buffers.
Generally, performance increases when you use more buffers. However, if system paging is heavy, the reverse might be true.
All buffers reside above the 16 MB line, whether you specify SAM or EXCP processing with the ICACC keyword (as described in ICACC). SAM processing allocates a set of buffers for every output image copy data set you request. EXCP processing allocates one set of buffers for all output image copy data sets, regardless of the number of image copies you request.
For more information, see Output-image-copy-write-options.