True for some value of "basically", but not true always. Keyed searches cannot be executed in ECKD mode, so a PDS directory, VTOC, or keyed BDAM or BSAM file that has lots of keyed searches done against it should be allocated on a cylinder boundary for a small improvement in elapsed time of the I/O. Bill Fairchild
----- Original Message ----- From: "Ted MacNEIL" <eamacn...@yahoo.ca> To: IBM-MAIN@LISTSERV.UA.EDU Sent: Thursday, September 4, 2014 12:45:39 PM Subject: Re: Allocation in CYLinder increments (UNCLASSIFIED) Since ECKD came out in the 1990's, the need to "worry" about the cylinder vs track allocation basically went away with "define extent". - -teD - Original Message From: Storr, Lon A CTR USARMY HRC (US) Sent: Thursday, September 4, 2014 13:30 To: IBM-MAIN@LISTSERV.UA.EDU Reply To: IBM Mainframe Discussion List Subject: Allocation in CYLinder increments (UNCLASSIFIED) Classification: UNCLASSIFIED Caveats: NONE Hello List, I'd be interested in feedback regarding allocation in tracks versus cylinders for certain types of high-usage datasets. I believe that there may be certain instances when allocation in units of CYL is beneficial. One example, I believe, is a PDS that has a multi-track directory: a single channel program can search up to a CYLinder at a time. Another example, I believe, is a VSAM dataset allocated in CYLinders will receive a CA-size of one CYLinder. A benefit similar to the first, if it even exists, would be achieved by caching the PDS directory in some way (e.g. BLDL), as I'm sure many system software applications already do (e.g. LLA and ISPF). Are there still pertinent benefits to allocating certain types of datasets in CYLinder increments? Thanks, Alan 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 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
