On Sat, 20 May 2017 11:09:18 -0700, Gerhard Adam wrote: >I don't see how the space would not be wasted. Where would it be assigned or >accounted for? If you ignored such waste, you could have more capacity >available than the volumes you've defined. > >On May 20, 2017, at 10:40 AM, Charles Mills wrote: > >>> if you write a 32K block to an emulated 3390 track, the balance of the >> space will be wasted >> >> Is that true? (Serious question -- everything I know about DASD management >> could be written in one paragraph of an e-mail.) Sure, it wastes "virtual" >> space on the emulated 3390 track, no doubt, but aren't modern storage arrays >> smart enough not to waste the real disk space that you are paying for on >> empty 3390 track space? >> It depends on the implementation. Some virtual disks use a compressed back end. It's likely that such a design would not store the track balance, or if storing it would compress it nearly to oblivion. The virtual capacity may exceed the real storage.
Some VM/370 (or so) paging systems depended on rotational latency -- they'd actually do a read without a search. I know of one early solid state disk product (ccd-based) that needed delays artificially inserted to accommodate that. So, your virtual disk can be not slow enough. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
