Good summary and analogy, Jim. Digging to the underlying *reason*, I believe that the MVS mindset is that what's physically on disk must match the logical odd or variable sizes (80 bytes and such). In the MVS world the concept of disk and the concept of filesystem are blurred.
Along come new software systems like Linux. Voi-la! there is a new market for whatever a channel-attched disk is. Now there is a screaming case for FBA DASD. And this ignores the old step children (VSE and VM) who would have benefitted from FBA decades ago. In keeping with your analogy, requiring that channel-attached disk all be CKD is like requiring that your steel 2x4s be filled, not hollow. I want to use the channel to get to that backing store without the CKD emulation on the disk end and companion de-emulation logic on the Linux end. [interleaved responses follow] > Actually, it is a well know economic law. If people > don't buy it, why support it? Right. But there is a new market. > When os/370 came out, it introduced a fixed block file > system (VSAM) now standardized at 4K blocks, eerily similar to ... > Few people bought them because most of their data were > in odd size blocks, mostly multiples of 80 and they > didn't want to have a mix of devices - some for VSAM > and paging and some for the rest of their data. ... Right. See my comment about blurred concepts. > Its pretty much the same reason people buy 2x4's > (boards). That's a standard and its been around a very > long time, so housing and building construction is > based on a standard wood 2x4, even if the material is > steel! A hollow steel 2x4 is stronger than a solid > wood 2x4, but the measurement is still a 2x4! Thanks. -- R;
