Configuration Types and Diagnostic Examples

 

Configuration types

     Type 1

      Type 2

      Additional configurations

Diagnostic Examples

 

Type 1 configuration

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

 


Type 2 configuration

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

 

 

 

Diagnostics and examples

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

Debugging example sequence

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.

  1. One controller is off-line. In the example shown in Figure 5, controller B is off-line.

Figure 5. Off line controller B

  1. 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

  1. 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:

  1. NIC or iSCSI Host adapter.
  2. Ethernet cables
  3. Switch
  4. RAID controller

 

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