Sun Storage 3310 Array
 
Sun Storage 3320 SCSI Array
 

GCS>Sun Microsystems>Storage - Disk>Modular Disk - 3xxx Arrays
 

- To configure a RAID controller drive array as a single bus configuration, connect the SCSI
jumper cable between the SCSI ports labelled "CH 0 OUT" and "SINGLE BUS CONF".

- To configure an expansion unit as a single-bus configuration, connect the SCSI jumper cable between SCSI
ports labeled <SB>, i.e. between the SCSI B IN port and SCSI A OUT port.

- By default there are 6 disk drives connected to channel 0 (drives 7-12).  Setting Single Bus
configuration places all 12 disk drives on channel 0 SCSI bus, i.e. adds the remaining 6 disk
drives (1-6) to channel 0.

Dual Bus Configuration:

- To create a dual-bus configuration on a RAID array, use the SCSI jumper cable to connect the CH 2 I/O port to 
the DUAL BUS CONF port.

- No jumper cable is required to configure the expansion unit for dual bus use.

- This configuration keeps the default six disk drives (7-12) connected to channel 0 SCSI bus, and places the
remaining 6 disk drives (1-6) on channel 2 SCSI bus.

- There is a limit of 16 drive id's per channel.  Therefore, with a 12-drive array, DO NOT connect dual bus channel 
0 or channel 2 (6 drive ids) to a single bus expansion unit (12 drive ids).

Since all disks are visible to both controllers at all times and all logical drives (luns) can
be assigned to either controller, what advantage does the dual bus configuration provide
The answer is, the dual-bus configuration provides the highest array performance. To achieve this selecting disks, 
creating luns, assigning luns to controllers, and mapping luns to channels, should be done correctly.  If you do this, 
the throughput can be optimized 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 0-3 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[TM] 320 HBA on the hosts you will have a potential throughput of 320 MB/s
from each host on a 3320. On a 3310, the potential throughput will always be 160 MB/s for either

the Ultra[TM] 160 or 320 HBA.
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.

Another advantage with the dual bus configuration is that we can use one set of drives to mirror the second set of 
drives configured as RAID1 drives.

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