On Fri, 6 Dec 2013 12:41:39 -0600, Dyck, Lionel wrote: > >Having a large a blksize with many small members results in many blocks with >wasted space. Having a small blksize with many large members results in >unnecessary I/O to read all the blocks of data. > I don't believe the usual access methods will ever write blocks containing unused space (perhaps null segments with RECFM=VBS?) But since track balancing is not routinely performed except by Binder, there's likely to be an average of BLKSIZE/2 unused space at the end of each track.
On Fri, 6 Dec 2013 15:30:37 -0500, Gerhard Postpischil wrote: > >In practice I've found the optimal block size to be close to half track, >with one exception (either 3K or 7K record size?), where five block per >track actually gave better usage. > I believe from the 3390 Ref and some trial and error that it's about 7K, with 7 blocks per track. And SDB actually selects that number. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
