HP EVA Array iSCSI Connectivity Option - Manual (Page 100)

The iSCSI Initiator may use all virtual paths as if they were physical paths following the rules/restrictions
of the iSCSI multipath software residing on the iSCSI Initiator.
The iSCSI Initiator host can have single or multiple physical connections or links to the IP storage network.
With a single physical connection, the iSCSI virtual paths can share the same link, because IP packets
with their TCP/iSCSI payloads are routed via the IP packet network addressing information.
With multiple physical connections, the MS iSCSI Initiator control panel applet allows setting a specific
link to be used as the primary iSCSI session during target login. However, the remaining links are
considered to be standby and will only be used if the primary link becomes unavailable.
This becomes an implicit hardware failover capability, because the initiator's routing table contains all
available links to the target. If the session's link becomes unavailable, the iSCSI session ends. TCP tries
another link in the routing table to renegotiate or connect to the mpx100/100b GbE port; the iSCSI
Initiator and the target performs their login sequence, and I/O resumes.
Configuring multipath with Windows iSCSI Initiator
Since V2.0 the Microsoft iSCSI Initiator includes support for establishing redundant paths for sending
I/O from the initiator to the target. Setting up redundant paths properly is important to ensure high
availability of the target disk. Ideally, the PC would have the paths use separate NIC cards and separate
network infrastructure (cables, switches, mpx100's/100b's). Separate target ports are recommended,
but are not necessary.
Microsoft MPIO support allows the initiator to log in to multiple sessions to the same target and aggregate
the duplicate devices into a single device exposed to Windows. Each session to the target can be
established using different NICs, network infrastructure, and target ports. If one session fails, another
session can continue processing I/O without interruption to the application. The iSCSI target must support
multiple sessions to the same target. The Microsoft iSCSI MPIO DSM supports a set of load balance
policies that determine how I/O is allocated among the different sessions. With Microsoft MPIO, the load
balance policies apply to each LUN individually.
The Microsoft iSCSI DSM assumes that all targets are active/active and can handle I/O on any path at
any time. There is no mechanism within the iSCSI protocol to determine whether a target is active/active
or active/passive; therefore, the mpx100/100b supports only multipath configurations with the EVA
XL and the EVA GL with active/active support.
Microsoft MPIO multipathing support for iSCSI
Installing the MPIO feature for Windows Server 2008
NOTE:
Microsoft Windows 2008 includes a separate MPIO feature that requires installation for use. Microsoft
Windows Server 2008 also includes the iSCSI Initiator. Download or installation is not required.
To install the MPIO feature for Windows Server 2008:
1. Check the box for Multipath I/O in the Add Features page ( Figure 49 ).
2. Click Next and then click Install.
100 Setting up the iSCSI Initiator for multipathing