Redundant Controller
10-12
D.Traffic Distribution and Failover Process
The diagram below illustrates a four-channel configuration using
channel 0 as the communications path. Channel 1 serves as the host
interface and multiple IDs are created to facilitate active-active
operation. Each controller occupies either a Primary ID or a
Secondary ID on drive channels. One logical unit is assigned to the
Primary controller and the other the Secondary controller. In the
event when one controller fails, the existing controller will inherit IDs
from the failed controller and continue I/Os.
Figure 10 - 9 Traffic Distribution
Logical Drive 0 Logical Drive 1
Host LUN Mapping ID0 / LUN
* (PID)
ID1 / LUN
* (SID)
Logical Drive Assignment Primary Secondary
Drive Channel 2 3
When creating a logical unit, users will be prompted to assign the
logical unit either to the Primary or to the Secondary controller. Once
the assignment is done, logical unit(s) assigned to the Primary
controller can only be mapped to the Primary IDs on host channel;
Logical unit(s) assigned to the Secondary controller can only be
mapped to the Secondary IDs on host channel.
The channel ID (Primary/Secondary) assignment for a SCSI controller
should look like this:
Primary Controller ID Secondary Controller ID
Host Chl SCSI ID PID = 0 SID = 1
Drive Chl SCSI ID 7 (or 8 for the dual
redundant chassis)
6 suggested (or 9 for the
dual redundant chassis)
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