[Info-vax] ISAM on disk layout. Was: Re: HP wins Oracle Itanium case

[JF Mezei]

Jan-Erik Soderholm wrote:

> Even more so in todays SAN's where you get a number of "gigs"
> out of some undefined disk array. Placement of files, as in
> MVS and other older systems, is mostly an non-issue today,
> from a performance standpoint. The fact that MVS still needs
> BLOCKSIZE, LRECL and so on, is mostly a compatibility issue.


As I recall, blocksize and LRECL has more to do with IBM's equivalent to
RMS than to disk organisation for DASD (hard disks).  When a COBOL
program opens a disk dataset, the blocksize probably discates size of
buffers and how many physical blocks are to be read for each logical
read operation etc.

However, when writing/reading to tape, tghe blocksize does matter
because mag tapes still let you specify a physical block size (as is the
base for VMS backup BTW).