TSM 6.3: Database Cache Hit Ratio Is Too Low

ISSUE

CAUSE

In TSM 6.3, there are two possible reasons: 1) The physical memory is too low, 2) The TSM server has been rebooted recently, and the cache hit ratios needs a few days to increase up to 98.

SOLUTION

Increase the physical memory if it is case 1). Just leave it, the warning should stops after a few days if it is case 2).

REFERENCE

IBM Tivoli Storage Manager, Version 6.3

Database manager tuning

Proper tuning of the database for IBM® Tivoli® Storage Manager is essential for optimal performance. The Tivoli Storage Manager database manager enables self-tuning memory.

Key areas to address when determining your Tivoli Storage Manager database manager configuration are:

• The database manager (instance-level) configuration parameters
• Database configuration parameters that have the largest impact on the performance of the system
• Maintenance operations that you must perform to ensure that the system continues to perform optimally once you have it running

Configuration parameters

The primary considerations for the Tivoli Storage Manager database are: enough memory for the database manager server, configuration of enough physical disks to handle the input/output (I/O) requirements, and enough CPUs to handle the workload.

Self tuning memory

For the best database manager operation remember, that the data and indexes are manipulated in the database buffer pools allocated in memory. Performance is stifled by a lot of paging operations required when there is more buffer pool space defined than real memory. Beside the buffer pools which use the most memory, the sort list, the lock list and the package cache are other memory segments allocated by the database manager.The database manager enables self tuning memory by default. This automatically samples the workload and performance characteristics of the database. Using this feature the database manager adapts the sort heap, lock list, package cache, buffer pool and total database memory improving performance and through put as your environment requires. Tivoli Storage Manager mixes the database workload between transactions recording backups to heavy query usage during restore operations.For information on tuning a lock list, see the technical document titled Managing the DB2 LOCKLIST Configuration Parameter with Tivoli Storage Manager.

Enough disk to handle I/O

Efficient performance relies on having enough physical disk drives to service the throughput required for the workload. The correct relationship of physical disks to CPU in the database manager server helps to maintain good performance. One of the most CPU intensive and database intensive parts of the Tivoli Storage Manager server workload is inventory expiration. There should be a ratio of one database directory, array, or LUN for each inventory expiration process.

CPUs to handle the workload

The power of the database manager system depends on the number and speed of its CPUs. For a balanced system, under normal operations only consume approximately 80% of the available CPUs.