Configuration
Types and Diagnostic Examples
Configuration types
The identifying features of a type
1 configuration (as shown in Figure 1)
are:
- Host
adapters are connected directly to one port
of Controller A and B, with
one or more host adapters per system.
This will provide increased bandwidth in addition to limited path/HBA
redundancy (assuming MPIO capability is present on the server).
- Multiple
servers can be connected, but without system-to-system failover (no MSCS).
However, access to the storage is still available in the event that one of
the servers and its associated path malfunction.
- In
a dual-controller environment, limited redundancy can be achieved in the
event that a controller goes offline. Adding an HBA/NIC to each of the
servers will provide additional path and HBA/NIC redundancy (assuming MPIO
capability is present on the server).
- To
isolate server resources some type of isolation mechanism, such as configuring
the Access Control List (ACL), should be used.
Figure 1.
Type 1 configuration

Single Controller

Dual Controller
The type 2 configuration can occur with or without
switches, as shown in Figure
2 and Figure
3.
Figure 2.
Type 2 configuration - with switches

The identifying features of a type 2 configuration are:
- Multiple
host adapters are connected for full redundancy across systems having
failover support such as MSCS.
- Host
adapters are connected either directly to ports or through switches.
Figure 3.
Type 2 configuration - without switches

In a type 1 configuration there are no external
switches. If a QLA4010 HBA is being used, the diagnostic tool available is the
SAN Blade Control IX application. This application provides configuration
management as well as diagnostic PING and read/write buffer test.
If a generic NIC is being used, the management and diagnostics are specific to
that card. In this case you can still use the PING
command from a system prompt. On the controller side, you can use the PING
command to verify the path from the controller to the host. If you intend to diagnose a failed path while
using the alternate path for production, be sure that you are familiar with the
tools so that the correct portion is being exercised and you do not unplug
anything in the active path.
For a type 2 configuration, use the features of the
switches and the capability of MSCS to isolate resources from the bad or
marginal path before beginning debug activities. Switches allow a view of log
information that shows what problems have been occurring, as well as
diagnostics that can be initiated from these managed elements. Also, a type 2
configuration has the capability to have more than one RAID controller unit
behind a switch. In the diagnostic maps, the switches are referred to
generically as concentrators. Figure 4
shows a type 2 configuration with two dual controller DS300 enclosures.
Figure 4.
Type 2 configuration with two DS300 enclosures

An example sequence for debugging a type 2 MSCS
configuration is shown in the following sequence of figures.
You can attach multiple server pairs to the switches by using Virtual
LANs (VLANs) for pair isolation or combinations of
type 1 and type 2 configurations. Break the larger configuration into its
smaller subelements and work with each piece
separately. In this way you can remove the good path and leave only the bad
path, as shown in the following sequence.
- One
controller is off-line. In the example shown in Figure
5, controller B is off-line.
Figure 5.
Off line controller B

- All
I/O is flowing through controller A. Controller B is now off line and can
be debugged. This yields the diagram shown in Figure
6 for debugging.
Figure 6.
All I/O flowing through controller A
Controller A is processing I/Os and is unavailable for diagnostics

- To
see more clearly what is involved, redraw the configuration showing the
path elements in the network, as shown in Figure
7.
Figure 7.
Path elements

The elements of the paths shown in Figure
7 are as follows:
- NIC
or iSCSI Host adapter.
- Ethernet
cables
- Switch
- RAID
controller
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