If I do dump to DASD, how much space do I need?

The maximum size of a single-volume DASD dump data set depends on the type of data set.

Conventional sequential data sets can span 65,535 tracks, and can hold approximately 3 GB.
Extended format data sets are supported by z/OS® V1R6 and later releases. Extended format sequential data sets can hold 16,777,215 blocks. The maximum size for extended format sequential is approximately 383 GB. You cannot use striping or compression options for extended format sequential data sets. You must use the guaranteed free space option to require DFSMS to reserve space at the time that the data set is created.
Note: Beginning in z/OS V1R12, SADMP supports placement of dump data sets in cylinder-managed space. In releases prior to z/OS V1R12, stand-alone data sets must remain in track-managed space.
Large format data sets are supported by z/OS V1R7 and later releases. Large format (DSNTYPE=LARGE) data sets can span 16,777,215 tracks. The maximum size for large format data sets is 768 GB.

If you require more space than you want to allocate on a single volume, you can define a multi-volume DASD dump data set that can span up to 32 volumes of the same device type.

Use the AMDSADDD REXX utility or the SADMP dump data set utility on the IPCS dialog to allocate and initialize a single volume DASD dump data set or a multi-volume DASD dump data set. This prepares the data set for use by the system where initialization is performed and for other systems that have access to the same data set using the same device numbers. For more information, see:

When using a multi-volume DASD dump data set, the device number of the first volume is specified. The other volumes are located by stand-alone dump using the information that is placed in the data set when it is initialized. All volumes are written concurrently by stand-alone dump. The data set is rejected if stand-alone dump is unable to access all volumes of the data set or if invalid control information is read from the data set during initialization.

If you do not allocate enough space in your dump data set, the stand-alone dump program prompts the operator to continue dumping to another DASD dump data set or tape volume. You can continue dumping to any stand-alone dump supported device, however, after a tape device is selected, it must be used to complete the dump even though multiple volumes might be required.

IBM® recommends that you allocate multiple dump data sets to perform a complete stand-alone dump.