Space on one volume
Enough space must be available on one volume to satisfy the primary
request. If not, the system terminates the job or searches another
volume, depending on the type of volume request made:
- Specific volume request: If the first volume
specified does not have enough space available, the job is terminated.
When extending a multivolume data set, if enough space is not available
to satisfy the secondary allocation on the second volume specified,
the job is terminated.
- Nonspecific volume request: If the first
volume chosen by the system does not have enough space available,
the system chooses another volume and continues to search for
space, asking for volumes to be mounted if necessary. The system
continues to search for space until it finds a volume with enough
space, exhausts all eligible volumes, or the operator cancels the
job.
Note: For a new indexed sequential data set, if
the first volume chosen by the system does not contain enough space
for the request, the system does not try to find space on another
volume, if the request is as follows:
- A request for multiple volumes or units.
- A request is for the second, third, or subsequent DD statement
used to define the data set.
Extents
The system tries to allocate the primary and secondary quantity
in contiguous tracks or cylinders. If contiguous space is not available,
the system satisfies the request with up to five noncontiguous extents (blocks) of space.
Multivolume data sets
When creating a multivolume data set, the primary quantity cannot
specify more space than is available on the first volume. If the
primary quantity requests all of the available space on the first
volume, the secondary quantity requests space on the subsequent
volumes.
Primary requests in blocks
If you request space in terms of average block length, the system
will compute and allocate the smallest number of tracks (or cylinders
if ROUND is specified) to contain the number of blocks specified
in primary-qty. blklgth will be used as the block length in this
computation, with the exception of the value zero. If a blklgth
of zero is specified for the first subparameter, the system uses
one of the following as the block length to compute the number of
tracks to allocate, in the order indicated:
- The blocksize from the DCB parameter, if specified
- The system determined blocksize, if available
- A default value of 4096.
System assigned space requests with
user labels
If user labels are specified, LABEL=(,SUL), the system allocates
up to four noncontiguous extents of space. The system allocates,
separately from the primary quantity, one track for user labels.
This one track is considered an extent.