For a complete discussion about V/VB/VS/VBS and F/FB/FBS file formats, please look at Chapter 20 of the DFSMS Using Data Sets manual. The following for FBS is extracted from that manual. This is the definitive manual for standard files to be processed by BSAM and QSAM.
Standard Format During creation of a sequential data set (to be processed by BSAM or QSAM) with fixed-length records, the RECFM subparameter of the DCB macro can specify a standard format (RECFM=FS or FBS). A sequential data set with standard format records (format-FS or -FBS) sometimes can be read more efficiently than a data set with format-F or -FB records. This efficiency is possible because the system is able to determine the address of each record to be read, because each track contains the same number of blocks. A standard-format data set must conform to the following specifications: v All records in the data set are format-F records. v No block except the last block is truncated. (With BSAM, you must ensure that this specification is met.) If the last block is truncated, the system writes it where a full size block would have been written. v Every track except the last contains the same number of blocks. v Every track except the last is filled as determined by the track capacity formula established for the device. v The data set organization is physically sequential. You cannot use format-FS for a PDS or PDSE. Restrictions If the last block is truncated, you should never extend a standard-format data set by coding: v EXTEND or OUTINX on the OPEN macro v OUTPUT, OUTIN, or INOUT on the OPEN macro with DISP=MOD on the allocation v CLOSE LEAVE, TYPE=T, followed by a WRITE v POINT to after the last block, followed by a WRITE v CNTRL on tape to after the last block, followed by a WRITE If the data set becomes extended, it contains a truncated block that is not the last block. Reading an extended data set with this condition results in a premature end-of-data condition when the truncated block is read, giving the appearance that the blocks following this truncated block do not exist. Standard-format data sets that end in a short block on magnetic tape should not be read backward because the data set would begin with a truncated block. A format-F data set will not meet the requirements of a standard-format data set if you do the following: v Extend a fixed-length, blocked standard data set when the last block was truncated. v Use the POINT macro to prevent BSAM from filling a track other than the last one. Do not skip a track when writing to a data set. Standard format should not be used to read records from a data set that was created using a record format other than standard, because other record formats might not create the precise format required by standard. If the characteristics of your data set are altered from the specifications described above at any time, the data set should no longer be processed with the standard format specification. format specification. Chris Blaicher Principal Software Engineer, Software Development Syncsort Incorporated 50 Tice Boulevard, Woodcliff Lake, NJ 07677 P: 201-930-8260 | M: 512-627-3803 E: [email protected] www.syncsort.com<http://www.syncsort.com/> INTEGRATING BIG DATA... SMARTER ________________________________ ATTENTION: ----- The information contained in this message (including any files transmitted with this message) may contain proprietary, trade secret or other confidential and/or legally privileged information. Any pricing information contained in this message or in any files transmitted with this message is always confidential and cannot be shared with any third parties without prior written approval from Syncsort. This message is intended to be read only by the individual or entity to whom it is addressed or by their designee. If the reader of this message is not the intended recipient, you are on notice that any use, disclosure, copying or distribution of this message, in any form, is strictly prohibited. If you have received this message in error, please immediately notify the sender and/or Syncsort and destroy all copies of this message in your possession, custody or control. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
