On Thu, Apr 18, 2002 at 07:23:55AM +0800, John Summerfield wrote: > > S/390 does also have FBA (fixed block architecture) DASD devices. > > Sadly, even in the Linux world these are not widely known or used. > > I maintain that they should be employed heavily and heartily! > > The benefits are numerous.
Oh? Like what? Remember that, these days, most DASD is made up of huge RAID arrays emulating either classic FBA or CKD devices, and the emulation overhead of either is pretty small. > Back when I was a sysprog we used VS1, and that had no support for FBA > devices (I think the 3370 was supported on MVS back then). MVS never has supported any FBA devices. The problem is that the CKD architecture is heavily embedded deep in two critical pieces of the MVS core: program fetch and VTOC processing. I'm not familiar with the details of PDSEs for program fetch, but if load libraries are PDSes, they're still searched by SEARCH KEY CCWs. > I'm sadly out of touch with mainframe hardware; it seems strange to me > I can get 120 Gbyte disks for my PC and you folk are using 2.3 Gbyte > drives on your mainframes. I know the theoretical limit is larger than > that, and was back when S/360 was announced. The limit is that the cylinder number is a halfword, and exceeding that breaks a LOT of things. There are even today things you can't put on a 3390-9 beyond cylinder 65535 (the JES2 spool dataset springs immediately to mind). OTOH, MVS shops ran into the need to span volumes a long time before others did, and so they understand how to manage multivolume datasets very well.
