VSP Gx00 Cache Details Test

This test reports the percentage of data that is yet to be written to the cache, and thus sheds light on a potential cache overload or a slowdown while writing data from the cache to the disk.

Target of the test : A Hitachi VSP Gx00 Series storage device

Agent deploying the test : A remote agent

Outputs of the test : One set of results for every logical cache partition on the Hitachi VSP Gx00 Series device monitored

The figure below depicts the test configuration page of this test. Click on the parameters in the figure below to know what they are and how to configure them.

Measures made by the test
Measurement Description Measurement Unit Interpretation

Cache usage rate:

Indicates the percentage usage of this cache switch to cache memory access path.

Percent

A very high value or a value close to 100% for this measure could indicate that the access path is over-utilized, probably owing to a slow data write rate to the cache. Comparing the value of this measure across paths could indicate which path(s) is choking.

Data could be transferred slowly over a path if cache does not have enough space to accommodate the data. Such an event could occur if the cache is unable to write data to the disk quickly; a slowdown in writes to disk can severely hamper the cache’s ability to make space for data waiting to be written, thus crowding the access path.

Write pending rate:

Indicates the ratio of write-pending data to cache memory capacity.

Percent

A high value of this measure or a value close to 100% is a cause for concern, as it indicates that too much data is yet to be written to the cache. This essentially means that the cache does not have enough space to accommodate the pending data. Such an event could occur if the cache is unable to write data to the disk quickly; a slowdown in writes to disk can severely hamper the cache’s ability to make space for data waiting to be written, thus rendering the write data pending for a long time.