On Thu, 18 Aug 2011 03:11:13 +0000, Ted MacNEIL wrote:
>I thought there was a minimum of 18 bytes for LRECL.
>At least, there was in 1981, when I learned JCL.
>
That was for tape, not DASD. And it applied to BLKSIZE, not LRECL.
I just allocated:
Device type . . . . : 3390
Data class . . . . . : **None**
Organization . . . : PS Current Utilization
Record format . . . : F Used blocks . . . . : 0
Record length . . . : 1 Used extents . . . : 0
Block size . . . . : 1 [selected by SDB; I specified 0]
1st extent blocks . : 86
Secondary blocks . : 23 Dates
Data set name type : Creation date . . . : 2011/08/17
SMS Compressible. . : NO Referenced date . . : 2011/08/17
Expiration date . . : ***None***
(I didn't try writing anything to it.) The restriction was due to access
methods' ignoring short tape blocks as noise. I've often wondered
what would happen if I allocated RECFM=VB,BLKSIZE=8192,
LRECL=137, all perfectly legitimate on tape, then wrote a single
5-byte record (plus BDW is 9) then CLOSEd the data set. Of
course, modern tapes and controllers are too smart to let that
cause problems -- they likely write and verify a preamble on each
block. But antiquated access method code might still look at the
CSW and reject the block as noise.
>-----Original Message-----
>From: Paul Gilmartin <paulgboul...@aim.com>
>Sender: IBM Mainframe Discussion List <IBM-MAIN@bama.ua.edu>
>Date: Wed, 17 Aug 2011 19:43:19
>
>BTW, I misstated the condition in my riddle earlier: "... what is the smallest
>block size
>that SDB will ever choose on a 3390?" Of course, for RECFM=F,LRECL=1, SDB will
>choose 1. But that's trivially uninteresting. I meant to say, "What is the
>smallest
>block size that SDB will choose on a 3390 for a blocked RECFM such as VB or FB
>(or perhaps U)?" The answer may be surprising at first.
-- gil
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