Chapter 3: Host Connection 57
Mixed
Topologies
The following table describes which of the components in this topology are
non-redundant and present a risk of a single point of failure. The following figure
shows an example of a mixed topology; that is, a topology that combines both switch
topology and direct-attach topology. This example shows three hosts, a controller
tray, and two switches.
The example in the figure identifies HBA1 and HBA2 on each host as connecting
points. For other configurations, these connecting points might be Ethernet adapters
for iSCSI connections, or a combination of one HBA and one iSCSI Ethernet adapter.
Switches are not supported for SAS host connections.
When a host is connected to a dual-controller controller-drive tray or a dual-controller
controller tray, each attached host should have two host adapters installed. The host
adapters might be HBAs for Fibre Channel or SAS, or Ethernet for iSCSI. For
redundancy, attach each of the host adapters that connects through a switch to a
different switch (or switch zone) so that one switch (or zone) connects to controller A
and the other to controller B in the controller tray or the controller-drive tray. In the
case where a host has one HBA and one iSCSI Ethernet adapter, the two connections
might require two different types of switches. Redundancy for a host that attaches
directly to a controller tray or a controller-drive tray requires that each host adapter
attach to a different controller.
ATTENTION Possible loss of data access – You must install alternate path software
or an alternate path (failover) driver on the host to support failover in the event of an
HBA failure or a host channel failure.
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