Where do the -71 and -16 come from? - Ted MacNEIL eamacn...@yahoo.ca Twitter: @TedMacNEIL
-----Original Message----- From: "Storr, Lon A CTR USARMY HRC (US)" <lon.a.storr....@mail.mil> Sender: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> Date: Thu, 21 Nov 2013 19:11:58 To: <IBM-MAIN@LISTSERV.UA.EDU> Reply-To: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> Subject: Re: Extents limit for HFS (UNCLASSIFIED) Classification: UNCLASSIFIED Caveats: NONE According to my personal notes The restriction of 127 extents per volume (device) comes from the DEB: DEBLNGTH is the number of double-words in the DEB (up to 255 ===> 255 * 8 = 2040; (2040 - 71) / 16 = 123). The restriction of 59 volumes (devices) per DD comes from the TIOT: TIOELNGH is the number of bytes in the TIOT entry (up to 255 ===> (255 - 16) / 4 = 59) Alan -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of DASDBILL2 Sent: Thursday, November 21, 2013 1:45 PM To: IBM-MAIN@LISTSERV.UA.EDU 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" <jwgli...@gmail.com> To: IBM-MAIN@LISTSERV.UA.EDU 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 <ee...@us.ibm.com> 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 lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN Classification: UNCLASSIFIED Caveats: NONE ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
