Optimizing-QoS-vSphere_final

Dependent Hardware iSCSI Adapters
Dependent hardware iSCSI adapters
depend on VMware networking and iSCSI
congurationandmanagementinterfaces
provided by VMware. This type of adapter
can be a card that presents a standard
networkadapterandiSCSIofoad
functionality for the same port. The iSCSI
ofoadfunctionalitydependsonthe
host’snetworkcongurationtoobtainthe
IP,MAC,andotherparametersusedfor
iSCSI sessions. An example of a dependent
adapter is the iSCSI-licensed Broadcom
5709NIC.HardwareiSCSIadaptersmight
need to be licensed to appear in the
vSphere Client or vSphere command-line
interface. A hardware iSCSI adapter is a
third-partyadapterthatofoadsiSCSIand
network processing from the host.
Dependent Hardware iSCSI
Adapter Limitations
The following limitations relate to the use
of dependent hardware iSCSI adapters:
•IPv6configurationcannotbe
used with dependent hardware iSCSI
adapters.
•No DHCP:DHCPcannotbeusedwith
dependent hardware iSCSI adapters.
• Routing is not available for
dependent hardware iSCSI adapters.
• The iSCSI
traffic resource pool shares do not apply
to iSCSI traffic on a dependent hardware
iSCSI adapter.
• A traffic-shaping
policy is defined by three characteristics:
average bandwidth, peak bandwidth,
and burst size. Traffic-shaping policies do
not apply to iSCSI traffic on a dependent
hardware iSCSI adapter.
• When a
dependent hardware iSCSI adapter is
used, performance reporting for a NIC
associated with the adapter might show
little or no activity, even when iSCSI
traffic is heavy. This behavior occurs
because the iSCSI traffic bypasses the
regular networking stack.
• If any security
vulnerabilities exist in the iSCSI device
software, data can be at risk through no
fault of ESX. To lower this risk, network
administrators should install all security
patches that the storage equipment
manufacturer provides and limit the
devices connected to the iSCSI network.
Dependent Hardware iSCSI Considerations
from VMware Regarding Dependent
Hardware iSCSI Adapters
When dependent hardware iSCSI adapters
are used with ESX, certain considerations
apply:
•WhenanydependenthardwareiSCSI
adapter is used, performance reporting
for a NIC associated with the adapter
might show little or no activity, even
when iSCSI traffic is heavy. This behavior
occurs because the iSCSI traffic bypasses
the regular networking stack.
•SomedependenthardwareiSCSI
adapters perform data reassembly
in hardware, which has a limited
buffer space.
•WhenadependenthardwareiSCSI
adapter is used in a congested network
or under load, network administrators
should enable flow control to avoid
performance degradation. Flow control
manages the rate of data transmission
between two nodes to prevent a fast
sender from overrunning a slow receiver.
For best results, enable flow control at
theendpointsoftheI/Opath,atthe
hosts and iSCSI storage systems.
•SomedependenthardwareiSCSIadapters
donotsupportIPv6andJumboFrames.
Check VMware’s documentation for
specific adapter limitations.
Note that other feature incompatibilities
mayexistwhenusingofoadengines.
For example, vCenter Server Heartbeat*
isincompatiblewithTCPOfoadEngine
(TOE), a common feature of some non-
Intel 10GbE cards. Because vCenter
Server Heartbeat is intended to manage
thepassingorlteringofselectedIP
addresses, the following TOE features
must be disabled on all network adapters
prior to installing vCenter Server Heartbeat:
•OffloadIPSecurity
•OffloadTCPSegmentation
•OffloadTCP/IPChecksum
Using VMware NetQueue with Intel VMDq,
VMXNET3,PCIeGen2x8connections,
andLBTwillprovidethehighestlevels
of performance so the next step of
monitoringbandwidthandtrafcwill
provide the best data on which to make
control decisions.

The key to understanding the needs
for QoS controls is to test the network
congurationwithbenchmarkingand
load-generation tools to determine
maximum throughput and typical or “real-
world” workloads. The basic rule here is
to understand the bottlenecks and assess
their impact.



Deploying the vSphere Management
Assistant (vMA) allows you to run
resxtop
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(remote esxtop) from the
command line and remotely connect
toESX/ESXihostsdirectlyorthrough
vCenter* Server to monitor various
aspects of performance. The Network
panel in resxtop displays server-wide
network utilization statistics.
Statistics are arranged by port for each
virtualnetworkdevicecongured.For
physical network adapter statistics, see
the row in Table 1 that corresponds to
the port to which the physical network
adapter is connected. For statistics on a
virtualnetworkadapterconguredina
particular VM, see the row corresponding
to the port to which the virtual network
adapter is connected.
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