IBM i integration
with BladeCenter and System x

Ethernet switches for iSCSI

IBM® BladeCenter® and System x™ servers that are attached to IBM i via iSCSI host bus adapters (iSCSI HBAs) typically require the use of Ethernet switches:

• For IBM i 5.4, a switch is required for the iSCSI network.
• For IBM i 6.1, a switch is optional for simple one-to-one iSCSI networks, but is required for more complex iSCSI networks.

Minimum requirements:

• 1 gigabit layer 2 switch, preferably dedicated to the iSCSI network and isolated from other networks.
• Copper and/or fiber optic ports consistent with your iSCSI HBAs.
• Any copper cables and premises wiring involved should be category 5e or category 6.
• Fiber optic connections may be preferred in environments with high electrical noise or longer cable length requirements. Fiber optic connections may cost considerably more than copper.
• Enough ports to accommodate all iSCSI HBAs and possibly the service processor connections too.
  (The service processor connection typically uses a separate network, and does not require gigabit speeds. See Ethernet switch requirements for the service processor connection below.)
• Switch ports should be 'access ports' rather than 'trunk ports'. Access ports are for device connections. Trunk ports are for connections to other switches.
  Note: It is highly recommended that Spanning Tree Protocol (STP) is turned off. If this is not done, the integrated server may fail to boot because STP typically introduces a large delay before the switch port goes into the forwarding mode. If Spanning Tree Protocol is still desired, then it may only be used if a special switch feature, such as Spanning Tree Portfast or STP Fast Start, is used so that the large delay is eliminated.

Optional features and considerations:

• 9000 byte jumbo frame support: The iSCSI network normally uses standard 1500 byte frames. It is possible to configure iSCSI HBAs to use larger frames on the iSCSI network. However, under heavy traffic, many switches do not perform well with larger frames, degrading performance of both storage and virtual Ethernet.
  If you are not sure that your switch performs well with larger frames, it is recommended that you use the default settings for 1500 byte frames.
  As long as switch limitations are not affecting performance, setting the iSCSI HBA and switch MTU configuration to 9000 typically improves performance, especially virtual Ethernet performance.
  If you plan to use jumbo frame support, you need to configure it on the switch, if not already enabled.
• Extra ports to accommodate future growth (for example, additional iSCSI HBAs per server or additional servers). iSCSI HBAs and hosted systems involved in hot spare need to be on the same switched network.
• Rack mounting capability.
• Managed switch functions provide additional features, such as the following:
  • Port mirroring to accommodate a sniffer – recommended.
  • Statistics support – recommended.
  • VLAN packet tagging (IEEE 802.1q).
    If your switch supports IEEE 802.1q VLAN, ensure that the switch is configured to treat the iSCSI HBAs as VLAN unaware (untagged) devices. This is also true for any service processor connection using the switch. This is generally the default behavior of new switches that support VLANs.
  • Special connections may be needed for the device providing the user interface.

Ethernet switch requirements for the service processor connection:

• Layer 2 switch with ports for copper cables.
• Typically part of an existing network with an i5/OS® LAN connection.
  See Considerations for connecting service processors to IBM i in the Information Center for some considerations that may affect how you decide to configure your network for i5/OS to service processor communications.

Ethernet I/O modules:

• BladeCenter Ethernet I/O module switches are normally used to connect the blade iSCSI HBAs to the Ethernet network. Most of the considerations listed in the External switch considerations section above also apply to Ethernet I/O module switches.
  Note: One of the available BladeCenter switch modules does not meet the minimum requirements stated in the External switch considerations section above, but can be used with restrictions. See the Problems with Blades Connected to System i via Server Connectivity Module software knowledge base article for more information.
• When Ethernet I/O module switches are used, a separate external Ethernet switch is not required. You can connect the Ethernet I/O module switches directly to the IBM i iSCSI HBAs if your environment does not otherwise require an external Ethernet switch.
• You can optionally use both Ethernet I/O module switches and an external Ethernet switch.

Pass-through I/O modules:

• BladeCenter pass-through I/O modules can be used to connect the blade iSCSI HBAs to the Ethernet network.
• When pass-through I/O modules are used, an external Ethernet switch is required for i 5.4 and for complex configurations in i 6.1, but optional for one-to-one configurations in i 6.1. See the External switch considerations section above.