User`s guide
PLANNING FOR HYPER-V
November09 Page12
Note: PowerConnect switches default to flow control being off. The Dell PowerVault
MD3000i storage array auto-configures to the switch when the flow control is
turned on.
UnicastStormControl
A traffic “storm” occurs when a large outpouring of IP packets creates excessive
network traffic that degrades network performance. Many switches have traffic storm
control features that prevent ports from being disrupted by broadcast, multicast, or
unicast traffic storms on physical interfaces. These features typically work by
discarding network packets when the traffic on an interface reaches a percentage of
the overall load (usually 80 percent, by default). Because iSCSI traffic is unicast
traffic and can typically use the entire link, disable unicast storm control on switches
that handle iSCSI traffic. However, the use of broadcast and multicast storm control
is encouraged. Refer to your switch documentation for information on disabling
unicast storm control
JumboFrames
Most enterprise gigabit-Ethernet equipment provides some support for jumbo frames.
Enabling jumbo frames accelerates iSCSI performance by about five percent and
reduces server CPU utilization by two percent to three percent with standard or
smarter NICs. You should enable jumbo frames on the switch ports that handle
iSCSI traffic. In addition, if a server is using a software iSCSI initiator-and-NIC
combination to handle iSCSI traffic, you must also enable jumbo frames on the NICs
to obtain the performance benefit and ensure consistent behavior.
Note: You must enable jumbo frames throughout the entire IP SAN from the NICs,
switches, and array ports; otherwise, behavior might be inconsistent. To
simplify troubleshooting initial deployments, make sure that the NICs,
switches, and storage arrays are fully operational before you enable jumbo
frames.
IP SAN Optimization for Throughput and I/Os
When designing your IP SAN, review the various factors in your network and the
applications that you are using. Consider these general rules when you design your
IP SAN.
To maximize the data throughput of your storage array, all data ports need to be
used. If your application is I/O intensive, use an iSCSI offload NIC. Consider
manually balancing your virtual disk ownership so that no single controller is
processing an excessive amount of I/O relative to the other controller. The Dell
PowerVault MD3000i storage system supports active/active controllers, with each
controller being able to simultaneous process I/O. The asymmetric design of the
controllers means that a virtual disk (logical unit number or LUN) is owned by a
controller, and all I/O access to the virtual disk is only possible through the owning
controller. To take advantage of both the controllers for I/O access, distribute virtual