Understanding single bus and dual bus configurations in the StorEdge 3310            

You must always have either the single bus or the dual bus channels cabled on the rear of
the array for proper  termination of the busses.  This is true even when using expansion units.

Since all disks are visible to both controllers at all times and all logical drives (luns) can 
be assigned to either controller and mapped to any of channels 0-3, what advantage does the 
dual bus configuration provide?

The answer is really nothing unless you are careful about which disks you create the luns on, 
to which controller you assign the luns, and to which channel you map the luns.  If you do it 
correctly you can optimize your throughput from the hosts to the luns by isolating I/O down 
only one array scsi bus through one array controller to one bank of disks on their own bus.

For example:

Channels 0-4 are all internally connected to both controllers by design.
Channel 0 is also internally on the same bus as disks 7-12 by design.
Both the dual bus and single bus channels are only connected internally to the same 
bus as disks 1-6 by design.

You then connect channel 2 externally to the dual bus channel putting disks 1-6 on their own 
scsi bus along with channel 2 but not connected to disks 7-12.
You attach 2 hosts to channels 1 and 3 respectively.

Then you create luns using only disks 1-6.
You create other luns using only disks 7-12.
You assign the luns on disks 1-6 to the primary controller.
You assign the luns on disks 7-12 to the secondary controller.
You assign the primary controller to channel 1.
You assign the secondary controller to channel 3.
And finally you map the luns on both controllers to give them a disk id.

With an Ultra 160 hba on the hosts you will have a potential throughput of 160 MB/s 
from each host.

Unless these rules are followed carefully, the host i/o will be greatly reduced with a total 
bandwidth of the 2 hosts will be at most 160 MB/s.  Of course, this is still very high 
compared to fibre channel which is around 8 MB/s on 100Gbyte hardware.