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Quick Tip - Using DASD

by L.M. Guttormson

This REXX exec gives the user an easy method for making efficient use of DASD when creating sequential files. A data set which contains 80 column cards blocked at 16,000 bytes uses only 48.14% of the useable track space on a 3380. The same file blocked at 23,440 (IBM's Half-track methodology) is using 99.82% of the usable space. Inefficient block sizes can easily cost a shop one out of every three packs used to store sequential data bases. This exec will calculate the optimum blocksize, perform a change to the JCL, and place the cursor to the right of the calculated blocksize so that you can go on your merry way without touching a calculator or pencil and paper.

/*REXX*/
/*                                                               */
/*To use this exec, put a question mark after the parameter for the
block size in your DCB statement. Then call this exec with your
record length as the parameter.                                  */
/*                                                               */
/* Example:  / /      DCB=(RECFM=FB.LREGL=134,Blksize=?          */
/*                                                               */
/*                                                               */
/* For the above example, on the command line enter "DCB 134".   */
/*                                                               */
/*                                                               */
ADDRESS  "ISREDIT"  "MACRO"  (LRECL )"
/*                                                               */
/* un-comment the next line for 3380 DASAD                       */
/*BLKSIZE = TRUNC (23482 / LRECL )                               */
/*                                                               */
/* un-comment the next line for 3390 DASAD                       */
/*BLKSIZE = TRUNC  (28076 / LRECL )                              */
/*                                                               */
BLKSIZE = BLKSIZE  *  LRECL
NEWBLK = "'BLKSIZE="  ||  BLKSIZE  ||  " '  FIRST":
ADDRESS USREDIT  "CHANGE 'BLKSIZE=?'   "NEWBLK;
EXIT

L.M. Guttormson, Galaxy Travel, Fort Lauderdale, Florida

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