Explanation: MAXEXTENTS(extents) is
an optional parameter specifying the number of extents that, if equaled
or exceeded, causes DFSMShsm to reallocate all non-VSAM data sets.
For extents, substitute a decimal number
from 0 to 16 specifying the number of extents to allow before DFSMShsm
does extent reduction. If you specify 0, DFSMShsm does not do extent
reduction.
When volume migration occurs for volumes containing a non-VSAM
data set that cannot migrate either because the data set was referred
to recently or has reached or exceeded its maximum extents, DFSMShsm
migrates and then immediately recalls the data set.
SMS relationship: Parameter differs in meaning when applied
to SMS-managed or non-SMS-managed DASD volumes or data sets.
SETSYS default: If you specify a value larger than 16, the
SETSYS default for extents is 16.
DFSMShsm default: If you do not specify this parameter on
any SETSYS command, the DFSMShsm default is 0.
Note: - The MAXEXTENTS parameter does not apply to VSAM data sets or to
data set organizations not supported by DFSMShsm.
- You use this parameter for active, non-VSAM data sets. This parameter
only applies to those non-VSAM data sets that are architecturally
limited to 16 extents. It does not apply to data
sets that are allocated to more than one volume, striped data
sets, extended format data sets, PDSE or HFS data sets. Data
sets that can be allocated to multiple volumes via the DATACLASS,
but are only allocated on one volume, are eligible for EXTENT REDUCTION.
- DFSMShsm will not do extent reduction unless the data set is more
than one day old in a single-DFSMShsm-host environment or two days
old in a multiple-DFSMShsm-host environment.
- Using a low MAXEXTENTS value might cause extent reduction to occur
more frequently than you want. If you specify a MAXEXTENTS value,
try using a value of 5 or more.