If possible, do this during scheduled outage though theoretically, this can be done even on a live system with minimum I/O.

Save NVRAM to disk. See Technical Instruction <Document: 1003584.1> (Sun StorEdge[TM] 3000 Series Arrays: Resetting the Minnow to Factory Default Settings or Saved Settings to the Disks.) for details on how to do this.

Do not insert the additional controller while the array is powered off.

The new controller will most likely have a higher serial number than the already-installed controller so if it is inserted while powered off it will become the master controller when it boots. This will reset the customer's array to defaults since the default values from the new controller will over-write the  NVRAM settings of the customer's controller.

Make sure that both controllers have their redundancy status set to enabled.

It has been found that a single controller with its redundancy status disabled will attempt to boot as a Master ( Primary) irrespective of whether it has a lower serial number or a higher serial number.

Slide in the second controller which is to be designated as the secondary.

The primary controller will synchronize with the secondary controller.This synchronization will take a few minutes.Please confirm the same via the telnet/serial interface to the array. Perform a Cntrl W to switch between the two controllers. In case the secondary controller does not have the same revision of controller firmware as the primary, re-insert the secondary controller to initiate the synchronization.

Be aware that only the controller firmware and NVRAM settings get synced over. Upgrade the SES and PLD revisions ( in the case of the Sun StorEdge[TM] 3510 FC or Sun StorEdge[TM] 3511 SATA array) if there is a mismatch which can be verified via the Sun StorEdge[TM] Configuration Service (SSCS) command line interface. Refer to the README of the latest Patch  ID: 113723 for the 3510, or Patch ID: 113724 for the 3511 for instructions.

To synchronize both the PLD and SES, you will need an outage. If it is required to only upgrade the SES firmware, it is possible to do so through a live upgrade of the SES firmware. Perform the download of the PLD and SES firmware according to the patch README. Please adhere to all the precautions as mentioned in the  README file.

Similarly, for the Sun StorEdge[TM] 33x0 array, the SAF-TE firmware will have to be brought to sync manually. Please follow all the instructions in the README of the Patch ID: 113722 for the 3310, or Patch ID: 113730 for the 3320.

Before any downloads, stop the Sun StorEdge[TM] Configuration Service Agent, if it is running. For information on the Sun StorEdge[TM] Configuration Service software please refer to the Notes below.

Give the controllers a few minutes to stabilize. It will be good if the actions are performed on the two array controllers alternatively so as to  give time for the controllers to stabilize.

Do not assume automatic mirroring of the cache. You will need to reset the controller to enable it.

Perform a Ctrl-W to make sure you can actually see the secondary controller after the setup is stable.

You might have to change the cache optimization policy to write-back since it has been recommended that single controller configurations should use the write-through policy to avoid data corruption issues. With a write-back policy , be aware that performance will not be the same as in a single controller set-up.

In an active-to-active configuration (standard configuration), we can assign any logical drive to either of the controllers, and then map the logical configurations to host channel IDs/LUNs. I/O requests from a host computer are directed to the primary or the secondary controller accordingly. The total drive capacity can be grouped into several logical configurations and assigned to both controllers so that they share the workload. This active-to-active configuration engages all array resources to actively maximize performance. An active-to-standby configuration is also available but is not usually selected in a dual controller set-up. By assigning all the logical configurations of drives to one controller, the other controller stays idle and becomes active only if its counterpart fails.

It has been seen that, sometimes on inserting the second controller, both the controllers may display bright green LEDs instead of the blinking LEDs to indicate the primary and steady green led for secondary. In such a circumstances, pull out the controller just inserted instead of performing any other action and insert the same again after a couple of minutes.

Sun StorEdge[TM] Configuration Service (SSCS) is a sophisticated program based on the Java[TM] programming language,which brings together storage configuration, resource allocation, maintenance and monitoring tools into one application for centralized administration of the array. It consists of a graphical user interface which can be invoked by running "/opt/SUNWsscs/sscsconsole/sscs".

The management of Sun StorEdge[TM] Array can be in-band using the SCSI / FC interface ( depending upon the array used) or be out of band using Ethernet interface.