The Diagnostics option allows a user to verify that a controller is functioning properly, through the use of various internal tests.
The Diagnostics use a combination of three different tests: Read Test, Write Test, and Data Loopback Test. You should run all three tests at initial installation and any time there are changes to the storage subsystem or components that are connected to the storage subsystem (such as hubs, switches, and host adapters).
Important: During the diagnostics, the controller on which the tests are run will NOT be available for I/O.
The Read Test initiates a read command as it would be sent over an I/O data path. It compares data with a known, specific data pattern, checking for data integrity and redundancy
A Write Test initiates a write command as it would be sent over an I/O data path (to the Diagnostics region on a specified drive). This Diagnostics region is then read and compared to a specific data pattern. If the write fails or the data compared is not correct, the controller is considered to be in error and is failed and placed offline. (Use the Recovery Guru to replace the controller.)
Important: The Data Loopback Test does not run on controllers that have SCSI connections between the controllers and drives.
The Data Loopback Test is run only on controllers that have Fibre Channel
Notes:
Running Controller Diagnostics