Specifications

Chapter 4 Subsystem Connection and Operation
Figure 4-11: Cascaded Subsystems to Clustered Servers
1). In the diagram above, the term “logical drive” is abbreviated as “LD.” The
host bus connection is identical to the previous diagram.
2). Each configured array (logical drive) is separately mapped (or associated)
with one host ID/LUN. Note that host mapping is separately done on
different RAID subsystems. Avoid using the same host IDs on any of the
SCSI buses linking these two subsystems.
3). If a server in a clustered pair fails or a host bus is disconnected, the
surviving server needs to access the arrays originally accessed by the failed
server. That’s why an array needs to be associated with IDs on two host
buses. In this way, every host bus has all mapped IDs. Most multi-pathing
or access management software running on clustered servers should be able
to manage the access to these IDs. See the arrows in the diagram above.
4). SCSI host adapters usually occupy SCSI ID 7. ID 7 is not available for
host bus mapping.
5). Each subsystem manages its own logical drives and ID mapping and will
not report ID conflicts with another subsystem.
6). Application servers see the logical configurations of disk volumes through
the unique SCSI bus IDs you selected for host mapping on each host bus.
Select different IDs for arrays on different subsystems.
Connection Topology 4-9