System Options under z/OS

BLKSIZE(device-type)= System Option: z/OS

Specifies the default starting point for block size calculations for new direct access bound libraries that reside in DSORG=PS data sets.

Default:	varies by device type
Valid in:	configuration file, SAS invocation, OPTIONS statement, OPTIONS window
Category:	File Control: SASFILES
PROC OPTIONS GROUP=	SASFILES
z/OS specifics:	all

Syntax
Details
See Also

Syntax

BLKSIZE(device-type)=value

device-type

specifies any valid specific device type number (such as 3380 or 3390), DASD, DISK, or OTHER.

DISK or DASD: indicates that the specified value is to be used as the default block size for all types of disk devices.
OTHER: specifies the value that SAS uses to allocate a library when the BLKALLOC option is specified and the BLKSIZE host option was not specified in the LIBNAME statement or LIBNAME function. See BLKSIZE= System Option: z/OS for more information.

value

specifies the default block size. Here are the valid values:

number: specifies the block size that SAS is to use for the device.
OPT: specifies that SAS is to choose the most efficient block size for the device and the type of library.
MAX or FULL: specifies that SAS is to use the maximum permitted block size for the device or 32760, whichever is lower.
HALF, THIRD, FOURTH, or FIFTH: specifies that SAS is to use the largest value that results in obtaining two, three, four, and five blocks per track, respectively.

Details

The following example tells SAS to choose optimum block size values for all disk devices except 3380s, for which one-third track blocking is requested:

options blksize(disk)=opt
        blksize(3380)=third;

For all DASD devices currently supported on z/OS, the default value of BLKSIZE(device-type) is HALF, which corresponds to the largest efficient block size that is supported by SAS and standard access methods.

When the library BLKSIZE is not specified by other means, such as with the library data set allocation or the BLKSIZE system option, SAS uses the block size value specified for the BLKSIZE(device-type) as a starting point for determining the block size. Constraints on the block size for direct access bound libraries might cause SAS to use a lower value than the specified value in some situations for direct access bound libraries. For more information, see Controlling Library Block Size.

Note: The BLKSIZE(device) option has no influence over the block size for sequential access bound libraries. [cautionend]