Allocating SYS1.DUMPxx data sets with secondary extents

Allocate SYS1.DUMPxx data sets using the following requirements:

Name the data set SYS1.DUMPxx, where xx is decimal 00 through 99.
Select a device with a track size of 4160 bytes. The system writes the dump in blocked records of 4160 bytes.
Initialize with an end-of file (EOF) record as the first record. (If you use ISPF 3.2 to allocate SYS1.DUMPxx data sets, the EOF record will be automatically written on the first track.)
Allocate the data set before requesting a dump. Allocation requirements are:
- UNIT: A permanently resident volume on a direct access device.
- DISP: Catalog the data set (CATLG). Do not specify SHR.
- VOLUME: Place the data set on only one volume. Allocating the dump data set on the same volume as the page data set could cause contention problems during dumping, as pages for the dumped address space are read from the page data set and written to the dump data set.
- SPACE: An installation must consider the size of the page data set that will contain the dump data. The data set must be large enough to hold the amount of data as defined by the MAXSPACE parameter on the CHNGDUMP command, VIO pages, and pageable private area pages.
  SVC dump processing improves service by allowing secondary extents to be specified when large dump data sets are too large for the amount of DASD previously allocated. An installation can protect itself against truncated dumps by specifying secondary extents and by leaving sufficient space on volumes to allow for the expansion of the dump data sets.
  
  For the SPACE keyword, you can specify CONTIG to make reading and writing the data set faster. Request enough space in the primary extent to hold the smallest SVC dump expected. Request enough space in the secondary extent so that the primary plus the secondary extents can hold the largest SVC dump. The maximum size of a data set is 65,535 tracks. For a 3390 this is 4369 cylinders, and will hold about 2.8 gigabytes of data. The actual size of the dump depends on the dump options in effect when the system writes the dump.
  Estimate the largest dump size as follows:
```
  Bytes of SDATA options + bytes in largest region size = Result1
```
```
  Result1 * number of address spaces in dump             = Result2
  PLPA * 20%                                             = Result3
  Bytes of requested data space storage                  = Result4

  Result2 + Result3 + Result4                  = Bytes in SVC dump
```
  Where:
  - Result1, Result2, Result3, Result 4: Intermediate results
  - SDATA options: Described in Contents of SVC dumps
  - PLPA: Pageable link pack area
For the size of the smallest dump, use the default options for the SDUMPX macro. The difference between the largest dump and the smallest dump will be the size of the secondary extent.

For example, to calculate the largest amount of storage required for a 3390 DASD, assume that, from the preceding calculations, the records needed for the SVC dump amount to 43200 kilobytes. There are 11 records per track and 15 tracks per cylinder. To determine the number of cylinders needed to allocate a data set of this size, do the following:

For 43200 kilobytes of storage, you will need space for 10800 SVC dump records (43200 / 4 kilobytes per record).
With 11 records per track, you will require 982 (10800 / 11 records) tracks.
Therefore, the data set would require 66 cylinders (982 / 15 tracks per cylinder) for allocation.
Note: If you are not receiving the dump data you require, increase the size of the dump data set. You will receive system message IEA911E.

The system writes only one dump in each SYS1.DUMPxx data set. Before the data set can be used for another dump, clear it using the DUMPDS command with the CLEAR keyword.

See z/OS MVS Programming: Authorized Assembler Services Reference LLA-SDU for information about the default dump options of the SDUMPX macro. See z/OS MVS System Commands for information about using the DUMPDS command.