On Fri, 19 May 2017 14:45:41 -0700, Gerhard Adam wrote: >z/OS doesn't emulate 3390's, the disk technology does. It also does so, for >good reason, because the biggest issue with DASD is differing geometries. >That would affect space allocation and the blocksizes that can be used. > At the very least, it's z/OS that impels a maximum block size of 32760 while the 3390 suports much larger.
>Since there is no performance penalty for emulating a 3390, there is zero >incentive for anyone to represent their disks as anything except a 3390. > I'm skeptical that layer(s) of emulation incur no performance penalty. Wouldn't a hypothetical emulated device supporting two 32760-byte blocks per track, or one 65535-byte block (the CCW count field) do better? Or eliminate an emulation layer and expose the underlying FBA to the (ststems) programmer. I believe recent OS releases have (very limited) support for this. An enhanced QSAM could make this transparent to the application programmer, even as QSAM does for z/OS UNIX files. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
