The IBM Support Center may request a CCWTRACE of I/O activity to examine the I/O to the DASD device. Do this by invoking GTF with the CCW, IO, IOSB, and SSCH options. Use the trace output to examine the data sent to and received from the DASD device by the VSAM block processor. See z/OS MVS Diagnosis: Tools and Service Aids for details about using CCWTRACE.