System Overview : Dell PowerVault 220S and 221S Systems Service Manual
file:///C|/Users/rishi_sood/Desktop/220s/en/sm/intro.htm[3/7/2013 12:09:13 PM]
Split-Bus Module
Your storage system supports three SCSI bus modes controlled by the split-bus module:
Joined-bus mode
Split-bus mode
Cluster mode
These modes are controlled by the position of the bus configuration switch when the system is turned on.
Figure 6
illustrates the switch position for each mode. For more information on
configuring the SCSI bus modes, see your
Installation and Troubleshooting Guide
.
Figure 6. Bus Configuration Switch Modes
1
joined-bus mode (
top
position for rack systems,
right
for tower systems)
2
split-bus mode (
center
position for rack and tower systems)
3
cluster mode (
bottom
position for rack systems,
left
for tower systems)
The only difference between cluster mode and joined-bus mode is the SCSI ID assigned to the enclosure services processor on the EMM. When cluster mode is detected, the processor
SCSI ID changes from 6 to 15. As a result, SCSI ID 15 is disabled, leaving 13 available hard drives in cluster mode. This allows a second initiator, such as a host bus adapter or RAID
controller card on a second host server, to use SCSI ID 6 (see
Table 4
for SCSI ID assignments and
Figure 7
for associated hard drives).
Table 4. SCSI ID Assignments
Configuration
Cables Used
SCSI IDs Used
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Joined-bus
1
H
S
Split-bus—primary EMM
1
H
S
Split-bus—secondary EMM
1
H
S
Cluster
2
S
H
H
NOTE:
The unshaded SCSI IDs are available for hard-drive use as indicated for each configuration. The reserved SCSI IDs are used as follows:
H = used by the host system initiator.
S = used by the storage system SES.
Figure 7. SCSI ID Numbers and Associated Hard Drives
