Appendix B. Deploying iSCSI host interface controllers on the IBM System Storage DS5000 series 525
Multipathing iSCSI
As with Fibre Channel SANs, iSCSI SANs, in concert with the DS5000 series, offer the ability
to provide failover to the alternate controller in the event of an outage situation. In addition,
many failover drivers, such as the native MPIO driver in the Windows 2003 and Windows
2008 operating systems, when combined with the IBM-provided DSM, also offer
load-balancing across available iSCSI routes between the target and the initiator as well.
Therefore, you still need to configure iSCSI with multiple NIC interfaces for optimal
performance and reliability for initiators connecting to a DS5300, DS5100, or DS5020 storage
subsystem.
Other iSCSI performance considerations
You must consider several other factors when working with a mixed-host interface
environment due to various limitations on the intermixing of the physical protocols at the
controller level and the host level.
A given host group must not contain hosts that are FC-based as well as hosts that are
iSCSI-based.
A single host must not be configured for both iSCSI connections and FC connections to
the storage subsystem.
The Remote Mirroring premium feature is only supported using FC connectivity.
Generically, even though both protocols are available within the storage subsystem itself, take
care that at the host and host group level, these protocols remain independent and are used
as a tiering strategy across the entire host pool rather than within a given host group or on a
singular host itself.
As described previously, FC and iSCSI provide radically different latency and throughput
capabilities, and this mixture within an initiator environment can be prone to failover driver
conflict, performance degradation, and data loss.
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