Obtaining an SVC dump

Obtain an SVC dump by:

• Using a SDUMP or SDUMPX macro in an authorized program.
• Entering the DUMP or SLIP operator command
• Setting a SLIP in the IEASLPxx parmlib member.

When z/OS® takes an SVC dump, it copies data into the DUMPSRV owned data spaces and high virtual storage. The collection of data can introduce an unusually heavy burden on storage resources. The virtual storage load remains until the dump is written out to a target data set on DASD. The data set can be:

• SVC dump data set that is specified on the DCB parameter of the SDUMP or SDUMPX macro.
• Pre-allocated SYS1.DUMPxx data set, or automatically allocated dump data set.

Use the DUMPDS operator command to manage the pre-allocated and automatically allocated data sets.

When an SVC dump occurs, if normal auxiliary storage use rises above 30%, the system might experience severe performance problems. The system might also experience an 03C wait state, which indicates that the system ran out of available paging slots. You can use the MAXSPACE and AUXMGMT options on the CHNGDUMP SET, SDUMP command to manage the burden of taking SVC dumps on a system. Using the options might not be sufficient to eliminate the problems that are associated with the restricted auxiliary (paging) storage.

• The MAXSPACE value restricts the virtual storage available to the DUMPSRV address space. When you use MAXSPACE, the installation must tune for the worst case usage of real and auxiliary storage. The following rules apply:
  • If the installation does not have a history that can be drawn upon, see Allocating SYS1.DUMPxx data sets with secondary extents for help in determining a maximum data set size. Use a multiple of the data set size to determine a MAXSPACE value. The installation must predict the size of the largest dump that it can configure.
  • The paging resources for the affected systems must also be increased to accommodate the additional load that is represented by the MAXSPACE value. The minimum value for defining the additional auxiliary storage capacity must be three times the MAXSPACE value. Adhering to the MAXSPACE guideline can maintain utilization within 30%.
• When you specify the AUXMGMT=ON parameter, the installation disregards first failure data capture (FFDC) to maintain system availability. The following rules apply:
  • No new dumps are allowed when auxiliary storage usage reaches 50%. New dumps can be initiated after the auxiliary storage usage drops below 35%.
  • Current SDUMP data capture stops when auxiliary storage usage exceeds 68%, and generates a partial dump.

For more information about setting the MAXSPACE or AUXMGMT value, see the CHNGDUMP Command in z/OS MVS System Commands.

In a sysplex, you probably need dumps from more than one system to collect all of the problem data. These dumps must be requested at the same time. To request multiple dumps, use the following procedures on any of the systems that might be part of the problem:

• Enter a DUMP command with a REMOTE parameter.
• Issue a SDUMPX macro with a REMOTE parameter.
• Create a SLIP trap in an IEASLPxx parmlib member in the shared SYS1.PARMLIB or in the parmlib on each system.
  • Sometimes you cannot predict which system has the problem. Use a ROUTE operator command to activate the traps on all systems with similar configurations. Each trap must include a REMOTE parameter to dump all the other systems that might be involved.