Parity Group Usage Test

A parity group is a group of hard disk drives (HDDs) that form the basic unit of storage for the TagmaStore USP and NSC subsystem. All HDDs in a parity group must have the same physical capacity. This test monitors the usage of the parity groups on the storage device.

Target of the test : A Hitachi USP storage device

Agent deploying the test : A remote agent

Outputs of the test : One set of results for every parity group on the Hitachi USP device monitored.

Configurable parameters for the test
Parameter Description

Test Period

How often should the test be executed.


The IP address of the host for which this test is to be configured.


The port at which the specified host is listening. By default, this is set to NULL.

UserID, Password and Confirm password

The test should be configured with the credentials of a special user account, which is specifically created for use with the export utility; this 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;

Provide the credentials of this user against the UserID and Password parameters. Confirm the password by retyping it in the Confirm Password text box.


Specify the duration (in seconds) within which the SNMP query executed by this test should time out in this text box. The default is 3 seconds.

Measurements made by the test
Measurement Description Measurement Unit Interpretation

I/O operations rate

Indicates the number of read-write operations performed on this parity group per second.


A high value for this measure is indicative of high I/O activity on the parity group. Comparing the value of this measure across parity groups can accurately reveal which parity groups are overloaded, and also enable administrators to easily detect irregularities in load distribution across the parity groups.

To uniformly balance load across parity groups, you should consider installing additional HDDs, or you can use volume migration to migrate volumes from high-usage parity groups to low-usage parity groups.

Transactions rate

Indicates the rate at which data transfers occur on this parity group.




Indicates the rate at which read operations are performed on this parity group.



Write IOPS

Indicates the rate at which data is written to this parity group.



Read hits

Indicates the percenatage of read requests serviced by this parity group.


Ideally, the value of this measure should be high. A low value is a cause for concern, as it indicates that a majority of read requests have failed.

Write hits

Indicates the percentage of data written to this parity group.



Cache-to-disk transfers

Indicates the number of data transfer operations performed from the cache to this parity group.


A high value for this measure is a sign of good health. A low value or a consistently decreasing value could be a cause for concern, as it indicates that the cache is not writing enough data to the disk; this in turn could overload the cache and hamper its ability to make space for data that is waiting to be written.

Response time

Indicates the current responsiveness of this parity group to I/O requests.



Ideally, the value of this measure should be low.

Transfer between disk and cache

Indicates the rate at which data transfer operations are performed between this parity group and the cache.