z/OS 1.5 introduced extent consolidation. The following is from z/OS DFSMS Using Data Sets SC23-6855-00:
VSAM Extent Consolidation The system consolidates adjacent extents for VSAM data sets when extending on the same volume. VSAM extent consolidation is automatic and requires no action on your part. If the extents are adjacent, the new extent is incorporated into the previous extent. Example: The old extent begins on cylinder 6, track 0, and ends on cylinder 9, track 14, and the new extent begins on cylinder 10, track 0, and ends on cylinder 12, track 14. The two extents are combined into one extent beginning on cylinder 6, track 0, and ending on cylinder 12, track 14. Instead of two extents, there is only one extent. Because VSAM combines the two extents, it does not increment the extent count, which reduces the amount of extents. HTH, Greg Shirey Ben E. Keith Company -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Doug Sent: Friday, May 22, 2015 4:19 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: SMS primary vsam space allocation Reread your post, I don't know if listcat " should " do that, just that if space is available for a second extent right behind , vsam will put the together as one . On May 22, 2015, at 17:13, Doug <dsh...@bellsouth.net> wrote: SMS consolidated the primary with secondary because they were allocated back to back Doug . On May 22, 2015, at 17:10, Ward, Mike S <mw...@ssfcu.org> wrote: Hello all, I know this is late on Friday before a three day weekend, however, I'm stumped by a problem. We have some vsam files that have a primary allocation of 398 cyls and a secondary of 398 cyls. The primary extent that is displayed with in a listcat says that it is 11940 wihich is double the primary, secondary extents are 5970 tracks which is correct for 398 cyls. Can someone tell my why this is happening on an SMS managed file. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
