Bill, You're right about the primary extent. I stand corrected My failing memory was confused. An extended format sequential dataset can also have 123 extents, can't it? Could it be that it isn't the primary allocation being able to take up to 5 extents to satisfy the request, but the 123rd extent. I just came across a note that states "The last four extents are reserved for extending a data set when the last extent cannot be allocated in one piece."
I also just saw a mathematical answer as to why the 123 extents in another post. So maybe the person (I believe a teacher in an IBM class eons ago) who first gave me the reason of the 'multiple physical extents to fulfill a logical extent request' may be an old tale. Rex -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of DASDBILL2 Sent: Thursday, November 21, 2013 12:45 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 The information contained in this message is confidential, protected from disclosure and may be legally privileged. If the reader of this message is not the intended recipient or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any disclosure, distribution, copying, or any action taken or action omitted in reliance on it, is strictly prohibited and may be unlawful. If you have received this communication in error, please notify us immediately by replying to this message and destroy the material in its entirety, whether in electronic or hard copy format. Thank you. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
