On Saturday, 09/12/2020 at 05:25 GMT, "John P. Hartmann" <[email protected]> wrote: > EDF came as an add-on to VM/370 release 6 in 1979. Along with FBA > support if memory serves.
I'm pretty sure that add-on was BSEPP or SEPP ([Basic] System Extensions Program Product, I think), which was subsequently rolled in with VM/370 to create VM/SP. I used to have a SEPP/BSEPP Redbook and I'm pretty sure it was there that the EDF file system was explained. But I may be misremembering. FWIW, that information was retained in the CMS Diagnosis Reference, last published with VM/ESA V2, as far as I can tell. (I'm trying to get the information resurrected before it's lost forever.) > Alan is not doing justice to the designers. Being copy-on-write, it was > the first CMS file system that had no leakage of disk blocks on crashes > or power outages. CDF had the choice of trashed files or block leakage > and clearly chose the latter, but as a consequence, you might have 10% > wasted blocks on a minidisk after a while. Ray Mansell recently noted over in IBMVM his contributions to EDF in the 80s. He's probably a good source of historical information. And I should point out that MVS sequential datasets (on which the CMS file system semantics are modeled) have similar restrictions. You cannot change the record length of an existing record in such a dataset (blocked or not). If I recall, ISAM provided a way to put records in logical sequence without dependency on physical sequence, allowing records to change length since a replacement record could be physically added anywhere there was space. This was subsequently replaced by VSAM RRDS. Alan Altmark Senior Managing z/VM and Linux Consultant IBM Systems Lab Services IBM Z Delivery Practice ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 [email protected] IBM Endicott
