The way VSAM handles error conditions , many I/O errors that cause COBOL program to abend  when we use non-VSAM access method do not cause an abend when we use VSAM.Instead the file status is being used to indicate the nature of the problem. Depending upon nature of the problem, an error message may or may not printed by VSAM in the spool and finally this might led to serious errors to go undetected.

Let us take an example where a serious error will occur and it will be un noticed. Suppoes a KSDS file is originally defined with 8000 records.Now if the file has grown upto 7800 records and next time when the program loads the VSAM file and if it has to load 4000rec records then VSAM will start writing the warning message after writing the first 200 records. the rest 200 records will not be written on the file  and job also completed successfully after writing the rest 200 warning messages in the spool and the last 200 transactions haven’t been added to the file.

The only way to avoid problem like this is to test the FILE  STATUS code after every I/O statements for a VSAM file to make sure that no error occurred. Use IF statement that test the file status codes.Then ,you can check for expected errors like no-record-found conditions as well as unexpected errors that cause the serious problems. The below list deals with the error handling rountines for VSAM file processings: