Split-bus module, Figure 6 – Dell PowerVault 220S (SCSI) User Manual
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System Overview : Dell PowerVault 220S and 221S Systems Service Manual
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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.
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
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