The 16 extents for non-vsam is obvious. The 59 volumes is a limitation of the TIOT. You have the 16 basic bytes of a TIOT entry and then 4 bytes for each UCB pointer. The TIOTLNTH field is a byte long, thus limited to 255. (Zero means end of TIOT.) 255-16=239 239/4=59
Why the 123 extent limit for VSAM? Beats me, but it is probably also related to control block structure limits 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] -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of DASDBILL2 Sent: Thursday, November 21, 2013 1:45 PM To: [email protected] Subject: Re: Extents limit for HFS I think there was some rational explanation given several years ago. Check the archives, John. Something about how many whatevers could fit within one such-and-such, where both are control blocks within a VSAM catalog structure. I disagree with the other post that mentioned up to five different extents to satisfy the primary size. If this were true, then we wouldn't have a limit of 16 extents for a non-VSAM data set, but rather 12 (16 minus 4). Each of those five extents that might be necessary to fulfill the primary request count towards the total, whether the total is 123 or 16. And, since the primary request could also be fulfilled with only one extent, then there can still be 122 more non-primary extents in a VSAM data set. Bill Fairchild Franklin, TN ----- Original Message ----- From: "John Gilmore" <[email protected]> To: [email protected] Sent: Thursday, November 21, 2013 11:11:46 AM Subject: Re: Extents limit for HFS Why the magic number of 123 extents per volume? 127 is more plausible. What else is going on here? On 11/21/13, John Eells <[email protected]> wrote: > > z/OS DFSMS Using Data Sets, topic 3.9.2.1, "Creating HFS Data Sets": > > ... > > These data sets can expand to as many as 255 extents of DASD space on > multiple volumes (59 volumes maximum with 123 extents per volume). > John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN 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
