There are some important differences when you use iSCSI, particularly regarding the LAN connection:
- iSCSI consumes almost all 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 microcode without stopping the system.
- When you use a 25-Gbps Ethernet channel board, make sure to define a redundant LU path. The 25-Gbps Ethernet channel board requires approximately 130 seconds at maximum before I/O restart for reboot during update of the channel board microcode or for reset if a failure occurs.
MTU values must conform to the following guidelines:
- 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 an iSCSI environment. As shown in the figure, the iSCSI target 00 is 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. As shown in the figure, 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. As shown in the figure, 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.
In an iSCSI environment, up to 4,096 LU paths can be defined for one iSCSI target, and up to 4,096 LU paths can be defined for one port.
The maximum number of iSCSI targets that can be created is 255 per iSCSI port.
When using iSCSI, an LU path cannot be defined for an intermediate volume.