Joined: 14 Jul 2008 Posts: 1249 Location: Richfield, MN, USA
Your question is a bit confusing. The members of a PDS have a common LRECL. The members don't have a BLKSIZE, the PDS has one. With a Physical Sequential file, the records have a LRECL and the file itself has a BLKSIZE. All this info is in the JCL Manual.
Joined: 06 Jun 2008 Posts: 8280 Location: Dubuque, Iowa, USA
LRECL is Logical RECord Length -- the length of an individual record (or the maximum size of an individual record for variable length records). BLKSIZE is the physical block size written to the hardware and consists of some number of records (1 minimum, maximum depending on the LRECL and other factors). Physical sequential files and members of a PDS have the LRECL of the file (eg, the record length of each individual record depends on the LRECL of the entire dataset but can vary); BLKSIZE is a characteristic of the entire dataset.
The directory of a PDS has no relationship to the LRECL of the PDS, as each PDS directory block is a 256-byte area.
So to answer your question, BLKSIZE is the physical length of data written to disk or tape and that block contains a number of logical records each no more than LRECL bytes long (and fixed at LRECL bytes long for fixed length files). These definitions apply to PS and PDS files.
Continuing, whenever you read data from disk, you read data, block after block. So if for your PDS (for example of course) has blocksize which can have 10 records, there are read always 10 records even when you want to read only one record.