On 2017-05-21, at 10:15, Jesse 1 Robinson wrote: > > So why not define all blocks as 32K? For other than FB, that makes sense, and > SDB algorithms take that into account. For RECFM FB, however, there would be > an egregious amount of unusable space on each 3390 track. Nothing in z > architecture can handle splitting a fixed block across tracks. Leftover space > on a track cannot be used for anything else. So generally SDB recommends > half-track blocking for FB data. Maximum data transfer per I/O, minimum > wasted track space. > The same considerations apply to RECFM=VB, assuming in both cases that LRECL is small compared to track capacity. (Of course, for RECFM=FB BLKSIZE must be a multiple of LRECL. A surprising case is RECFM=FB, LRECL=7000.)
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