With dual logging, updates are recorded in two log data sets. It is unlikely that an unrecoverable DASD failure will occur on both log data sets at the same time, so this option protects you from log failures. The database manager continues running as long as it can read from and write to one of the logs. With single logging, any I/O error on the log would cause it to end.
To establish dual logging at database generation time, you must define two VSAM clusters of equal size for the logs. The DLBL file name for the first log must be LOGDSK1, and for the second log LOGDSK2. When starting the application server to perform database generation, specify the initialization parameter DUALLOG=Y. Later, when starting the COLDLOG operation, specify it again.
If just one log was defined at database generation time, you can use the COLDLOG operation to establish the second log to the database. Define this log to be the same size as the first, and name it LOGDSK2 on the DLBL statement.
If you have been running with LOGMODE=A or L, take a database archive or log archive before starting the COLDLOG operation. (The COLDLOG operation reformats the original log, thus erasing all the existing log data.) An example of the job control statements for starting the COLDLOG operation to create a dual log is shown in Figure 74. Note that the LOGMODE is set to Y for a COLDLOG.
Figure 74. Example of a Job Control to Start the COLDLOG Operation
// JOB COLDLOG // EXEC PROC=DBNAME01 // EXEC PROC=ARIS71PL // EXEC ARISQLDS,SIZE=AUTO,PARM='STARTUP=L,SYSMODE=S,DUALLOG=Y,LOGMODE=Y' /* /& |