A single target iSCSI HBA installed in the iSeries™ system is capable of supporting several servers or hosted systems. Each initiator HBA in the System x or blade system is also capable of connecting to multiple target iSCSI HBAs.
You can configure the iSCSI environment to support multiple target iSCSI HBAs, multiple iSCSI initiator HBAs, and multiple storage connections.
Figure 8 illustrates a hosted system that is connected to more than one target iSCSI HBA in the iSeries system.
Figure 8 shows multiple iSCSI HBAs installed in the hosted system.
Paths
Paths are connection points between virtual devices and iSCSI HBAs in the iSeries system. A virtual device being hosted by i5/OS® is said to be linked to a path. Initiator iSCSI HBA ports access the virtual device through the path.
iSeries virtual storage or devices are linked to a network server host adapter (NWSH) object. For example, a configured virtual disk (such as Drive C:) hosted in i5/OS is linked to the NWSH that represents the target iSCSI HBA adapter.
There are several storage paths defined in Figure 8. These are labelled 1, 2 and M.
You can configure iSCSI-attached servers to use either an single path or a multipath group.
Single paths
Virtual storage or devices that are linked to a specific iSCSI HBA can only be accessed through that adapter.
In Figure 8, paths 1 and 2 represent specific target iSCSI HBAs in the iSeries system. Devices defined in path 1 can only be accessed by the iSCSI adapter port for which the path is defined. Similarly, devices defined in path 2 can only be accessed by the iSCSI adapter port for which the path is defined. Any devices that are linked to path 1 or 2 are said to be linked exclusively to that iSCSI HBA.
Multipath I/O and storage connection redundancy
A hosted system can use multiple iSCSI data paths to access virtual disks hosted by i5/OS.
You can configure a multipath group of two or more target iSCSI HBAs and then specify that a virtual disk should be accessed using the multi-path group instead of a single iSCSI HBA. With this configuration, the data on the virtual disk can be accessed using any of the iSCSI HBAs in the multipath group.
In Figure 8 the multipath group is defined as path M. The virtual disks that are linked to the multipath group can be accessed by any of the target iSCSI HBAs that are also linked to the multipath group. Only one multipath group can be defined per hosted system. This group can include up to four target iSCSI HBAs.
For the most reliable network you should do the following things:
The advantage of the multipath configuration is that, if there is a hardware failure, the hosted system can continue to access the disks that are configured to use the multipath group, using any of the iSCSI HBAs that are configured in the multipath group. This configuration can provide uninterrupted storage connections in case of a problem with a target iSCSI HBA, an initiator iSCSI HBA, or a switch.
See Configuring multipath I/O for more information about installing the required software components and linking storage for the integrated server.