W dniu 20.12.2025 o 01:08, Michael Watkins pisze:
From memory: No z/OS dataset can span more than 59 volumes. 16 extents can
reside on each volume unless the data set is SMS-managed and the DSNTYPE is
defined as 'EXTENDED', in which case up to 123 extents can reside on each
volume. However, unless Extent Constraint Removal is specified as 'Y' in the
DATACLAS, the total number of extents spanning all volumes is 255.
Not exactly.
Datasets are limited to 16 or 123 extents per volume.
Some datasets can be multi-volume, other datasets are single-volume
only. Maximum is 59 volumes (on DASD).
Some datasets are limited to 64k TRK per volume, other are not limited.
The limits depends on dataset organisation and type. Examples:
basic PS - 16 ext, 59 vol, 64k TRK
large PS - 16 ext, 59 vol, 16M TRK
extended format PS - 123 ext, 59 vol, no known limit for size.
PDSE - 123 ext, 1 vol, no practical limit for size.
VSAM - 123 ext, 59 vol, 4GB limit size (with exception for ZFS)
ext-fmt & ext-addr VSAM - 123 ext, 59 vol, 4G CI size (up to 128 TB),
other interesting features.
(the above is not full list)
SMS is pre-req for extended format, however as we can see it is not
pre-req for 123 extents.
Extent constraint removal is for VSAM only and for VSAM-specific limit
(255 ext per dataset or rather component).
--
Radoslaw Skorupka
Lodz, Poland
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