Network configuration for iSCSI

An iSCSI connection makes it possible to construct an IP-SAN by connecting many hosts and storage systems at a low cost. However, iSCSI greatly increases the I/O workload of the network and the storage system. When using iSCSI, it is very important that you configure the network so that the workload among the network, port, controller, and drive is properly distributed.

Even though the LAN switches and NICs are the same, there are some important differences when you use iSCSI, particularly regarding the LAN connection. You need to focus particular attention to the following:

  • iSCSI consumes almost all of the available Ethernet bandwidth, unlike a conventional LAN connection. This can significantly degrade the performance of both the iSCSI traffic and the LAN. Therefore, it is very important that you separate the iSCSI IP-SAN and the office LAN.
  • Host I/O load affects the iSCSI response time. In general, the greater the I/O traffic is, the lower the iSCSI performance.
  • Make sure you have a failover path between host and iSCSI, so that you can update the firmware without stopping the system.
NoteThe iSCSI ports do not support fragment processing (dividing a packet). When the maximum transmission unit (MTU) of a switch is smaller than that of an iSCSI port, packets might be lost, and data cannot be transferred correctly. The MTU value for the switch must be the same as or greater than the MTU value for the iSCSI port. For details of the MTU setting and value, see the user documentation for the switch.

The MTU value for the iSCSI port must be greater than 1500. In a WAN environment in which the MTU value is 1500 or smaller, fragmented data cannot be transferred. In this case, lower the maximum segment size (MSS) of the WAN router according to the WAN environment, and then connect to an iSCSI port. Alternatively, use a WAN environment in which the MTU value is greater than 1500.

The following figure shows LU paths configuration in a Fibre Channel environment. The figure shows the iSCSI target 00 associated with three logical volumes (00:00:00, 00:00:01, and 00:00:02). LU paths are defined between the two hosts in the iSCSI target 00 and the three logical volumes.

You can define paths between a single server host and multiple LUs. The figure shows that each of the two hosts in the iSCSI target 00 can access the three LUs.

You can also define paths between multiple server hosts and a single LU. The figure shows that the LU identified by the LDKC:CU:LDEV number 00:00:00 is accessible from the two hosts that belong to the iSCSI target 00.

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