VSAM R/M uses two types of control blocks:

• User control blocks (RPL, ACB, and EXLST)
• Control blocks built for record management by VSAM OPEN (all other control blocks)

The RPL's RPLFDBWD field (4 bytes at offset X'0C') provide valuable failure-related codes. A description of the return codes and reason codes can be found in z/OS DFSMS Macro Instructions for Data Sets.

The VSAM SNAP dump facility provides hexadecimal listings of some control blocks and data areas. To obtain a SNAP dump, perform one of the following tasks:

• Code the SNAP macro with the SDATA=CB option (described in z/OS MVS Programming: Authorized Assembler Services Reference ALE-DYN, z/OS MVS Programming: Authorized Assembler Services Reference EDT-IXG, z/OS MVS Programming: Authorized Assembler Services Reference LLA-SDU, z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO).
• Specify this option to ABDUMP with the CHNGDUMP operator command or the IEAABDnn or IEADMPnn members of SYS1.PARMLIB.

The SNAP dump facility is only available at SYSABEND time.