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

Configurable parameters for the test
  1. TEST PERIOD - How often should the test be executed.
  2. HOST - The host for which the test is to be configured.
  3. PORT - The port at which the device listens. By default, this is set to NULL.

  4. DKC SERIAL NUMBER - Specify the serial number of the target Hitachi VSP Gx00 Series storage device that is to be monitored.

  5. USERID and PASSWORD – To extract metrics from the target storage device, the eG agent should be configured with the credentials of a special user account, which is specifically created for use with the Java export utility. This user account should fulfill the following conditions:

    • Should not possess the ‘write’ permission;
    • Can be of any user type; however, to ensure that the eG agent collects statistics pertaining to all storage partitions, it is recommended that this user is of type storage administrator;

    Specify the credentials of such a user in the USERID and PASSWORD text boxes.

  6. CONFIRM PASSWORD - Confirm the password by retyping it here.
  7. TIMEOUT - Specify the duration (in seconds) beyond which this test should time out in the TIMEOUT text box. The default is 3 seconds.
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.