Out of curiosity, what is the PHYSICAL track size of modern disk (EMC, IBM, etc.). Is there an industry standard or is everyone different?
I would think that there is still some validity to matching I/O requests to the PHYSICAL geometry even with emulation, RAID, striping, cache, etc. Head movement must still count for something. ----------------------<snip>-------------------- >One could enlarge those data set if a new unit type with larger tracks >would be defined. > >I admit I'm too busy (lazy) right now to RTFM but would appreciate any >toughts on this (just curious). Why do we still keep the ~55k track >size and increase only the number of cylinders? With modern DASD >subsystems it shouldn't matter, right? What are the track size limits >in z/OS? I guess it's 64k, but still this would be 16% more. > > ---------------------<unsnip>----------------------- You're right, but the downside is this: there are literally millions of lines of JCL still in regular use that allocate space in terms of tracks and cylinders. To change the length of a track would invoke nightmares of geometry changes, which we all suffered through in pre-3390 days whenever a newer DASD design hit the street. IT managers that remember those days still cringe at the thought! Until all allocations are done in terms of bytes, or multiples thereof, a geometry change will put people into cold sweats. Old habits are hard to break; old nightmares are hard to forget. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
