There used to be a command on the CBT tape to do track capacity calculations.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List [IBM-MAIN@LISTSERV.UA.EDU] on behalf of Radoslaw Skorupka [r.skoru...@hotmail.com] Sent: Monday, October 25, 2021 11:39 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: VSAM: Why a CISIZE of 4KB has 12 phyrecs/Track, not 13? W dniu 25.10.2021 o 16:44, Oscar pisze: > Hi there, > > There's something I'm being missing, but acording to my numbers, there > should be 13, not 12: > > Bytes per track: 56,664 bytes > Bytes accessible per track: 55,996 bytes > CI size: 4096 > Physical record size: 4096 bytes > > Physical records per track (Bytes accessible per track / physical > record size): 55,996 / 4096 = 13.6708984375 = 13???? > > What I'm missing? You're missing CKD deep details. Instead of looking for old documentation just do some quick test: allocate single-track datasets. Each of them can be VSAM or just PS, it doesn't matter. However for PS it would be a little bit easier. Important: specify RECFM=F and LRECL=BLKSIZE=n, where n is any number you want to test. I would suggest the following: n=10 n=512 n=4096 Then use your ISPF editor to fill the datasets with some data. You will find out how many records/blocks fit on a track. Note: you won't get more than 86 blocks per track. Even very short ones. Reason? Gaps between blocks. More specifically: you block (physical records) consist of C and D. CKD is for Count Key Data. Your PS file has no K, so it is just C D. And gaps between them. And R0 which is also some physical record. And HA - Home Address, another 5-byte physical record. And 3390 is FBA under cover, with cell size=34B. And all the gaps or physical records (including C as separate entity) occupy one or more cells, not fraction. BTW: The above is part of "extra material" which I sometimes teach during VSAM course. -- Radoslaw Skorupka Lodz, Poland ---------------------------------------------------------------------- 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
