68 QXS G2 Hardware Installation and Maintenance Guide
Reverse Cabling/Straight-through Cabling for 2U Systems
Figure 62 provides an illustration of connecting RAID chassis and expansion chassis in a reverse
cabling (fault tolerant) and straight-through cabling configuration for 2U systems.
Figure 62 Reverse Cabling/Straight-through Cabling
Figure 62 (left) shows reverse cabling of a RAID chassis dual-controller 2U chassis and supported 2U
drive chassis configured with dual expansion IOMs. Controller module 0A is connected to expansion
module 1A, with a chain of connections cascading down (blue). Controller module 0B is connected to
the lower expansion module (9B), of the last expansion chassis, with connections moving in the
opposite direction (green). Reverse cabling allows any expansion chassis to fail—or be
removed—while maintaining access to other chassis.
The diagram at right (above) shows the same storage components connected to use straight-through
cabling. Using this method, if an expansion chassis fails, the chassis that follow the failed chassis in
the chain are no longer accessible until the failed chassis is repaired or replaced.
The 2U expansion chassis shown in Figure 62 can either be of the same type or they can be a mixture
of the 2U12 and 2U24 models. Given that supported expansion chassis models use 12Gb/s SAS
link-rate and SAS 3.0 expanders, they can be ordered in desired sequence within the system,
following the RAID chassis. The middle SAS ports (Port B) on expansion modules are not used. Refer
to Expansion Chassis IOM on page 19 for additional information.
Controller A
Controller A
Controller B
Controller B
Reverse Cabling/Fault Tolerant Straight-through Cabling
Add up to 9 expansion chassis
Add up to 9 expansion chassis
0A
0A
0B
0B
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
1A 1A
2A
2A
3A
3A
9A
9A
1B
1B
2B
2B
3B
3B
9B
9B
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