Maintaining a Storage Array 99Diagnosing a RAID Controller ModuleThe diagnose controller command’s testID parameter takes the followingoptions, which you can use to verify that a RAID controller module isfunctioning correctly:• 1— Reads the test• 2— Performs a data loop-back test• 3— Writes the testThe read test initiates a read command as it would be sent over an I/O datapath. The read test compares data with a known, specific data pattern,checking for data integrity and errors. If the read command is unsuccessful orthe data compared is not correct, the RAID controller module is considered tobe in error and is placed offline.Run the data loopback test only on RAID controller modules that haveconnections between the RAID controller module and the physical disks. Thetest passes data through each RAID controller module physical disk-sidechannel out onto the loop and back again. Enough data is transferred todetermine error conditions on the channel. If the test fails on any channel,this status is saved so that it can be returned if all other tests pass.The write test initiates a write command as it would be sent over an I/O datapath to the diagnostics region on a specified physical disk. This diagnosticsregion is then read and compared to a specific data pattern. If the write failsor the data compared is not correct, the RAID controller module is consideredto be in error, and it is failed and placed offline.For best results, run all three tests at initial installation. Also, run the tests anytime you make changes to the storage array or to components connected tothe storage array (such as hubs, switches, and host adapters).A custom data pattern file called diagnosticsDataPattern.dpf is included onthe Utility directory of the installation CD. You can modify this file, but thefile must have the following properties to work correctly for the tests:• The file values must be entered in hexadecimal format (00 to FF) withonly one space between the values.• The file must be no larger than 64 bytes in size. Smaller files can be used,but larger files can cause an error.
