If you have requested a buffer pool and have not used a BUILD or GETPOOL macro for the DCB by the end of your DCB exit routine, the system automatically allocates virtual storage space for a buffer pool. The buffer pool control block is also assigned and the pool is associated with a specific DCB. For BSAM and BPAM, a buffer pool is optional. You can request it by specifying BUFNO. For QSAM, BUFNO can be specified or permitted to default in the following ways:

If you do not code a non-zero value for MULTSDN on the DCBE macro:

n—Extended format but not compressed format and not LBI (n = 2 × blocks per track × number of stripes)

1—Compressed format data set, PDSE, SYSIN, SYSOUT, SUBSYS, UNIX files

2—Block size > =32␠760

3—2540 Card Reader or Punch

5—All others

If you code a non-zero value for MULTSDN on the DCBE macro, then see DASD and Tape Performance.

If you are using the basic access method to process a direct data set, you must specify dynamic buffer control. Otherwise, the system does not construct the buffer pool automatically.

If all of your GET, PUT, PUTX, RELSE, and TRUNC macros for a particular DCB are issued in 31-bit mode, then you should consider supplying a DCBE macro with RMODE31=BUFF.

Because a buffer pool obtained automatically is not freed automatically when you issue a CLOSE macro unless the system recognized your specification of RMODE31=BUFF on the DCBE macro, you should also issue a FREEPOOL or FREEMAIN macro (see Freeing a Buffer Pool).