Reason:
Setting the sysparm IOCHNBLK to the value 1 or allowing it to use the default value 1, causes Backup and Archive jobs to write only one block to a tape at a time. This causes the job to run slower and to use more processing time. Sysparm IOCHNBLK can accept a value from 1 to 9, which is the number of tape blocks to be written with one I/O. Setting a value of 9 generally improves the performance significantly. This exception will be cleared when this check runs again after the job causing the exception is changed and runs, or after the job statistics are older than the number of days specified in the AGE parameter for this health check. The default for the sysparm IOCHNBLK will be changed to 9 with the next release of CA Disk.
Action:
Setting the sysparm IOCHNBLK to 9 allows Backup and Archive jobs to better utilize I/O resources and to reduce run time. A higher number will reduce the number of EXCPs issued to the tape, reducing elapsed time due to tape channel conflicts. It increases the storage utilization by (n-1)*tape blocksize*2. The REGION size of the jobs should also be reviewed to ensure that it will support the increased requirements.
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