Monitoring the Efficiency of the Caching Mechanism

The cache efficiency is monitored at each level of the storage subsystem: each controller, logical drive and overall subsystem. The CacheHitRatio parameter represents the percentage of data blocks that were successfully served by the cache without directly interrogating the physical layer. Values in the lower range indicate that the cache size is probably not large enough to properly optimize the data flow in the SAN.

To evaluate the caching efficiency for a specific subsystem:

1.	Double-click the subsystem's CacheHitRatio parameter.

TREE_Subsystem_CacheHitRatio

Selecting the CacheHitRatio Parameter on a Subsystem

2.	A graph is automatically displayed to provide you with an history of the amount of memory used to cache the read and/or write operations on the subsystem.

GRAPH_CacheHitRatio

Graph – Cache Hit Ratio on a Subsystem

You can also create a query on each logical drive of the specific subsystem to determine which drive is the most called upon.

1.	Create a PATROL Query in the PATROL Console to show the value of the CacheHitRatio parameter of the SEN_I345_LOGICALDRIVE class; In the main menu bar, click Action > New Query…

QUERY_CacheHitRatio_General

PATROL Query – General Tab

2.	Enter the Query name (example: Logical Drives Caching)

3.	Enter the Query description (optional)

4.	In the Query Result Filter section, select Show Selected Objects and check the Parameters box

5.	In the Additional Filtering, select the Application Class level filtering and the Enable Parameter level filtering options

6.	Open the Application Class tab

7.	In the Pattern Matching section, select Like and type SEN_I345_LOGICALDRIVE

QUERY_CacheHitRatio_AppClass

PATROL Query – Application Class Tab

8.	Open the Parameter tab

9.	In the Pattern Matching section, select Like and type CacheHitRatio

QUERY_CacheHitRatio_Param

PATROL Query – Parameter Tab

10.	Click OK to display results of the query.