DADSM tracing - syncsort_allocation_control_center

When SMS attempts to obtain space from a volume in a storage group, SMS makes a call to a system component called DADSM. DADSM has two system exits that can be used by SMS/Debug: IGGPRE00 and IGGPOST0.

The DADSM preprocessing exit (IGGPRE00) gets control before the space attempt, and has the name of the candidate volume that was selected by SMS. SMS/Debug can use this exit to track which volumes have been selected by SMS.

Note: This exit is not typically used by SMS/Debug, but can be activated by SMSDEBUG=ALL.

The DADSM postprocessing exit (IGGPOST0) gets control after DADSM has made the attempt at obtaining space on a candidate volume. In most cases, the exit simply shows that DADSM successfully allocated the data set along with information about which volume was selected.

However, the SMS/DebugIGGPOST0 exit can be very useful for allocation failures. The product can examine and display the return codes available to the exit and display information about why a candidate volume failed. The following list illustrates some of the common reasons for failure:

Space not available on the volume
DADSM preprocessing exit rejected the volume
VTOC is full

Without SMS/Debug, the system will only display information about why the last candidate volume failed.

When SMS/Debug encounters a DADSM failure, the product always displays failure codes available to the DADSM postprocessing exit. For the more common failure codes, the product will display a text message about the failure.

The IGGPOST0 exit can be very helpful in debugging SMS allocation problems. To activate debugging using the postprocessing exit, specify either SMSDEBUG=YES or SMSDEBUG=ALL.

Note: Many other products use the DADSM exits. Depending on the start order of the products, and the internal logic for each product, the flow through the various DADSM exits can be affected. For this reason, DTS Software recommends that the SMS/Debug be started after other products that use DADSM exits.

Sample trace output

The following job shows sample output from the SMS/DebugDADSM trace facility.

// EXEC PGM=IEFBR14
//DD1 DD DSN=DON.DD1,SPACE=(TRK,1),SMSDEBUG=(NOACS,NOVOL,DADSM)
ACC00510-* STARTING TRACE FOR POST_DADSM-ALLOCATE, DSN=DON.DD1, VOL=SMS002, DD=DD1
ACC05201-* ALLOCATE FOR 1 TRACKS EXTENT 0 RC=0 - SUCCESSFUL

Figure 3-5. Sample SMSDEBUG DADSM trace output

DADSM tracing - syncsort_allocation_control_center - Latest

Syncsort™ Storage Management Sms/Debug User Guide

Sample trace output