Acquire/DASD captures disk occupancy details from IBM or compatible mainframes running z/OS.
IBM provides some information about disk occupancy, in the type 19 SMF records, but these are only produced by events such as switching SMF datasets or issuing a Z EOD command, and do not contain sufficient information for good reporting purposes.
Acquire/DASD captures data in one of two ways:
Cyclic mode
Acquire/DASD will read information from all online disks and pass records to the SMF subsystem and repeat this at an interval of the user’s choosing until instructed to stop by an operator command.
Single shot mode
Acquire/DASD will process DCOLLECT data that has been generated in another job or step, and will write out SMF-style records itself. When it has done this it will stop.
Acquire/DASD provides for the capture of information about datasets. You can use the DSG= and DSN= control cards to create up to 100 groups of dataset names, each with up to 100 dataset names, using simple string matching. If you intend to do this, you should experiment with Acquire/DASD in single shot mode to ensure you have sized the ACQDWK03 file correctly.
If you generate dataset groups, be aware that the values IBM provide in DCOLLECT data are not absolutely accurate for VSAM files, and especially for ICF catalogs allocated to the CATALOG address space. The net effect is that the sum of used and free space will probably not add up exactly to the total allocated for a group of datasets, although it should be no more than about 5–10% under the correct value.
By default, Acquire/DASD makes the free and used values match the totals. This is done by calculating the used space percentage, then adjusting the free space to match, for example:
Allocated = 55 GB
Used = 32 GB
Free = 25 GB
Total Used + Free = 57 GB - higher than the Allocated number.
Used % = 100 * 32/55 = 58.2%
We will make Free% = 100 - 58.2 = 41.8 %
Adjusted free space = 0.418 * 55 = 23 GB
You may turn this option off and have the “real” numbers by using a control card of DSGFIX=N.