You are configuring a Windows Server 2008R2 Hyper-V failover cluster. You configure five
iSCSI logical unit numbers (LUNs) on shared storage, and you present them to the first
server. Each LUN appears twice in the Disk Management console. You need to ensure that
each LUN appears only once in the Disk Management console. What should you do?
A.
Reset the iSCSI initiator name to the default name.
B.
Install and configure Microsoft Multipath I/O (MPIO).
C.
In the Disk Management console, rescan the disks.
D.
In the Disk Management console, configure shadow copies.
Explanation:
Consider using multipath I/O software: In a highly available storage fabric, you can deploy
failover clusters with multiple host bus adapters by using multipath I/O software. This
provides the highest level of redundancy and availability. For Windows Server 2008 R2, your
multipath solution must be based on Microsoft Multipath I/O (MPIO). Your hardware vendor
will usually supply an MPIO device-specific module (DSM) for your hardware, although
Windows Server 2008 R2 includes one or more DSMs as part of the operating system.
Multipath I/O Overview
Applies To: Windows Server 2008 R2
Multipathing Support for High Availability
WindowsServer®2008 includes many enhancements for the connectivity of a computer
running a Windows server-class operating system to storage area networking (SAN)
devices. Among the enhancements enabling high availability for connecting Windows-based
servers to SANs is integrated Multipath I/O (MPIO) support. Microsoft MPIO architecture
supports iSCSI, Fibre Channel and serial attached storage (SAS) SAN connectivity by
establishing multiple sessions or connections to the storage array.
Multipathing solutions use redundant physical path components — adapters, cables, and
switches — to create logical paths between the server and the storage device. In the event
that one or more of these components fails, causing the path to fail, multipathing logic uses
an alternate path for I/O so that applications can still access their data. Each network
interface card (in the iSCSI case) or HBA should be connected by using redundant switch
infrastructures to provide continued access to storage in the event of a failure in a storage
fabric component. Failover times vary by storage vendor, and can be configured by usingtimers in the Microsoft iSCSI Software Initiator driver, or modifying the Fibre Channel host
bus adapter driver parameter settings. New MPIO features in Windows Server2008 include a
Device Specific Module (DSM) designed to work with storage arrays that support the
asymmetric logical unit access (ALUA) controller model (as defined in SPC-3), as well as
storage arrays that follow the Active/Active controller model. Features of the included DSM
The Microsoft DSM provides the following load balancing policies. Note that load balance
policies are generally dependent on the controller model (ALUA or true Active/Active) of the
storage array attached to Windows based computers. Failover No load balancing is
performed. The application specifies a primary path and a set of standby paths. The primary
path is used for processing device requests. If the primary path fails, one of the standby
paths is used. Standby paths must be listed in decreasing order of preference (the most
preferred path first). Failback Failback is the ability to dedicate I/O to a preferred path
whenever it is functioning. If the preferred path fails, I/O is directed to an alternate path until
function is restored to the preferred path, but I/O automatically switches back to the
preferred path when function is restored. Round-robin The DSM uses all available paths for
I/O in a balanced, round-robin fashion. Round-robin with a subset of paths The application
specifies a set of paths to be used in a roundrobin fashion, and a set of standby paths. The
DSM uses paths from primary pool of paths for processing requests, as long as at least one
of the paths is available. The DSM uses a standby path only when all primary paths fail.
Standby paths must be listed in decreasing order of preference (most preferred path first). If
one or more of the primary paths become available, DSM uses the standby paths in their
order of preference. For example, given 4 paths — A, B, C, and D — A, B, and C are listed
as primary paths, and D is standby path. The DSM chooses a path from A, B, and C in
round-robin fashion as long as at least one of them is available. If all three fail, the DSM
uses D, the standby path. If A, B, or C become available, DSM stops using D and switches
to available paths among A, B, and C. Dynamic Least Queue DepthThe DSM routes I/O to
the path with the least number of outstanding requests. Weighted PathThe application
assigns weights to each path; the weight indicates the relative priority of a given path. The
larger the number, the lower the priority. The DSM chooses the path that has the least
weight from among the available paths. The Microsoft DSM preserves load balance settings
even after the computer is restarted. When no policy has been set by a management
application, the default policy that is used by the DSM is either Round Robin, when the
storage controller follows the true Active/Active model, or simple failover in the case of
storage controllers that support the SPC-3 ALUA model. With simple Failover, any one of the
available paths can be used as the primary path, and remaining paths are used as standby
paths.