-----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of Rick Fochtman Sent: Friday, March 05, 2010 12:33 PM To: IBM-MAIN@bama.ua.edu Subject: Re: Defrag
----------------------------------<snip>-------------------------------- ------ AFAIK, you are limited to 16 extents on a volume (NON-VSAM, PDS, DAM, etc.). If you are allowed (or can) do multi-volume, then yes, you get 16 [max] per volume for 59 volumes. Reclaiming space in the VTOC: If I can get all my space consolidated to just the DSCB #1, then all the other DSCBs (model 3s) become available, giving space for more allocations in the VTOC. If I remember correctly, there can be up to 4 Model 3 DSCBs to get you to 16 extents (for a data set) -- (non-VSAM, PDS, DAM, PS, etc.). Otherwise, once you have used up all the DSCBs in the VTOC, you can't allocate anything more, or even get a secondary extent on that volume. So defragging does recover space for a VTOC. --------------------------------<unsnip>-------------------------------- ------ I can't speak for Extended Format, but for non-Extended Format datasets, you can only have one FORMAT-3 DSCB per dataset (Except for the special case of ISAM, now long dead.) Rick <SNIP> Based on the doc, if an F1DSCB can only have 3 extents, and an F4DSCB can only have 4 extents, but a simple PS data set is limited to 16 Extents on a volume, then we have a problem. It has been 14+ years since I've had to do DSCB handling (OBS/ACS WYLBUR would try to get a PDS to a single extent...). So I don't recall the actual layouts and only went by what IBM's doc says. And I could very well have misread or misinterpreted DFP/DFSMS's verbiage. But the point was recovering space in a VTOC... Regards, Steve Thompson ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
