4. Operation › 4.4 Administering CA MICS › 4.4.8 CA MICS Administration in SMS-Controlled Environment › 4.4.8.5 System-Determined Block Size

4.4.8.5 System-Determined Block Size

System-determined block size can be a useful feature in
providing site-SMS conformance.  Using it must be moderated
by two considerations:

 o  Access method
 o  Intent of use

System-determined block size generally assumes that standard
access methods are employed according to DSORG.  Clearly,
this is not always the case.  SAS data libraries are a good
example.  As mentioned in Section 4.4.8.1, SMS Allocation of
SAS Data Sets, SAS data libraries are allocated with all the
external characteristics of a sequential data set.  However
their internal format is proprietary and cannot be read or
written properly at the record level using standard access
methods.

System-determined block size is designed to optimize
sequential access of large (that is, multi-track) files.  Its
"one size fits all" implementation does not tailor blocking
or buffering for performance efficiency.  SAS FORMAT catalogs
provide a good example of this.  Because DSORG=PS is
specified for these data sets, you may assume that half-track
blocking is the best option.  But these data sets don't
contain data, they contain executables.  Very large buffers
will be allocated and filled while the actual executable that
was requested is likely to be fairly small.  Examination of
the effect half-track blocking has on processing, in this
case, demonstrates that this choice causes very inefficient
memory use and increased SRB time.

The default forced block sizes delivered with the CA MICS
distribution libraries are already set for optimal operation.

See SAS Usage Notes V6-SYS.FILE-6849 and VS-SYS.FILE-7901 for
more information.