Joined: 08 Jun 2007 Posts: 71 Location: Zoetermeer, the Netherlands
Yep, it's called "SDB" (system determined blocksize). You code your application like you described, do not hard-code blocksizes in your JCL and the O.S. will determine the optimum blocksize for you, taking into account the DADS device on which the dataset is placed.
I worked in a componay once which had a mix of 3380 en 3390 disks. Works very cool.
1 catch: when you concatinate input datasets, you have to make sure they all have the same blocksize (so be sure there placed on the same type of DASD).
Joined: 22 Apr 2006 Posts: 6258 Location: Mumbai, India
When running under MVS, BLOCK CONTAINS 0 can be specified for QSAM files; the block size is determined at object time from the DD parameters or the data set label.
The BLOCK CONTAINS clause is an optional clause in a file description entry. The BLOCK CONTAINS clause specifies the size of the physical records. The characters in the BLOCK CONTAINS clause reflect the number of bytes in the record. (For example, if you have a block with 10 DBCS* characters, the BLOCK CONTAINS clause should say BLOCK CONTAINS 20 CHARACTERS.