Dell Networking 2024 Reference Manual page 538

Default Configuration
By default, frames are not remarked. The default vpt setting for iSCSI is 4,
which the default class of service 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.
In general, the use of iSCSI CoS is not required. 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 using the min-bandwidth settings.
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. The iscsi cos enable command enables
the generation of the iSCSI Application Priority TLV over DCBX using the
value set by the iscsi cos vpt command on switches that support
DCBX.
Example
The following example configures iSCSI packets to receive CoS treatment
using DiffServ Code Point AF 41 and configures remarking of transmitted
iSCSI packets.
538
iSCSI Optimization Commands