HP StorageWorks 1510i Modular Smart Array iSCSI concepts and deployment guide (431338-002, July 2008)

4Multipathing
In an iSCSI network, there is the possibility that any component between the server (initiator) and the
MSA1510i (target) might fail. These components include Ethernet NICs, switches, cables, and MSA
storage ports. To guarantee uninterrupted access to the storage in the event of a failure, a redundant
path must exist.
Included in this section:
• MSA1510i multipathing rules
• Path validation
• Example multipath configuration
NOTE:
For information on the Microsoft MPIO architecture and role of DSMs, see the whitepaper on the Microsoft
website: h
ttp://www.microsoft.com/WindowsServer2003/technologies/storage/mpio/default.mspx.
MSA1510i multipathing rules
The following rules must be followed for proper multipath operation of the MSA1510i:
• Two MSA1510i controllers must be installed in the MSA1510i.
• Tw o M SA 1510 i 2 - Po r t E t h e r ne t i SC SI I / O m od u l e s m us t b e i n s t a ll e d i n t h e M SA 1510 i.
• TheMicrosoftDSMmustbeinstalledineachserver.
• TheremustbeaminimumoftwopathsforeachinitiatortotheMSA1510istoragetarget(onefor
each controller).
• Redundant network topology must provide one network path from the server NIC to the primary
MSA1510i controller and a separate network path from the server NIC to the redundant MSA1510i
controller.
• All MSA1510i iSCSI targets accessible by an iSCSI initiator shall be equally accessible through the
same subset of physical iSCSI Ethernet ports per controller.
• All servers connected to the MSA1510i in multipath configurationsmusthavetheMicrosoftDSM
installed.
Path validation
Path validation in an iSCSI network is an important part of maintaining a valid redundant controller
configuration. Various tools are available to determine if a path is compromised. Some of the tools
include ping, switch management tools, link status, controller port status, controller ping support, and
Device Manager available in Windows. Each of these tools has a unique purpose when validating the
path. The foremost test to review path status is a review of the server content in Device Manager, if the
wrong number of devices are present, redundancy has failed.
Before troubleshooting can begin, a basic understanding of what is expected in the Device Manager is
necessary.
As shown in the following illustration, Box 1 identifies the physical devices reported from both controllers
of a single MSA. In this example, there are 16 physical devices, eight from the active controller login
and eight from the standby controller. Box 2 identifies the multipath devices that are abstracted from the
physical devices. The multipath devices are a logical device controlled by the Microsoft DSM, which
determines which actual physical device should receive the I/O.
1510i Modular Smart Array iSCSI concepts and deployment guide
39