VSP Cache Switch to Cache Memory Test

An access path is a path through which data and commands are transferred within a disk subsystem. Since data is written to the cache memory via a cache switch, the cache switch to cache memory route is also an access path. If there are too many writes still pending to the cache memory, you might want to know how the data transfer in this path is progressing to determine whether a slowdown in the path could have contributed to the high write-pending rate. The VSP Cache Switch to Cache Memory test monitors the usage of each cache switch to cache memory access path to facilitate such an analysis.

Target of the test : A Hitachi VSP storage device

Agent deploying the test : A remote agent

Outputs of the test : One set of results for every cache switch to cache memory access path on the Hitachi VSP 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. 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.

  5. CONFIRM PASSWORD - Confirm the password by retyping it here.
  6. TIMEOUT - Specify the time 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

Usage:

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.