I was in a class a long time ago and the explanation at that time was as follows, to the best of my recollection.
They can handle up to 127 extents, but any request for secondary can take up to 5 extents to satisfy it. The comment was that the developers didn't want to have to deal with the case where they were at, say, 125 extents and asked for another and got 5 back. In that case they would use 2 and have to give 3 back. It had something to do with they were using a service that wasn't theirs and didn't want to deal it. This way if it was at 122 extents and asked for another extend it would always fit be it 1 or 5 extents returned. As I said, this was from a long time ago and my page-in facility may have lost a few bits along the way. 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 John Gilmore Sent: Friday, November 22, 2013 8:53 AM To: [email protected] Subject: Re: Extents limit for HFS For the BLKSIZE= constraint mod(32760,8) = 0, mod(32767,8) ¬= 0. For the extents-per-volume question it is hard to see any basis for an alignment issue, and in any case both 123 and 127 are odd. (Of the two 123 is composite and 127 = 2^7 - 1 is a Mersenne prime, but this difference too is unlikely to be relevant.) Finally, my point was not a cavil. I have no animus against the number 123. I was and am seeking enlightenment. There is presumably a rationale for the number 123; but 1) what it is has eluded me; and 2) a search of the IBM-MAIN archives was unhelpful, perhaps because my query was inept. 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 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
