Dell PowerEdge M420 Reference Manual page 516

Parameter
remark
Default Configuration
By default, frames are not remarked. The default vpt setting for iSCSI is 5,
which the default classofservice dot1p mapping assigns to queue 2.
Command Mode
Global Configuration mode.
User Guidelines
The remark option only applies to DSCP values. Remarking is not available
for vpt values.
By default, iSCSI flows are assigned to the highest VPT/DSCP value that is
mapped to the highest queue not used for stack management or the voice
VLAN. Make sure you configure the relevant Class of Service parameters for
the queue in order to complete the setting.
Configuring the VPT/DSCP value sets the QoS profile which selects the
egress queue to which the frame is mapped. The default setting for egress
queues scheduling is Weighted Round Robin (WRR).
You may alter the QoS setting by configuring the relevant ports to work in
other scheduling and queue management modes via the Class of Service
settings. These choices may include strict priority for the queue used for
iSCSI traffic. The downside of strict priority is that, in certain circumstances
(under heavy high priority traffic), other lower priority traffic may get starved.
In WRR the queue to which the flow is assigned to can be set to get the
required percentage.
If an EqualLogic array is detected when QoS is enabled, two additional TCP
ports receive preferential QoS treatment (TCP ports 25555 and 9876). This
QoS policy is applied globally.
516
iSCSI Optimization Commands
Description
Mark the iSCSI frames with the configured DSCP when
egressing the switch.