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Application of Quality of Service to iSCSI Traffic Flows
You can configure iSCSI CoS mode. This mode controls whether CoS (dot1p priority) queue assignment
and/or packet marking is performed on iSCSI traffic.
When you enable iSCSI CoS mode, the CoS policy is applied to iSCSI traffic. When you disable iSCSI CoS
mode, iSCSI sessions and connections are still detected and displayed in the status tables, but no CoS
policy is applied to iSCSI traffic.
You can configure whether the iSCSI optimization feature uses the VLAN priority or IP DSCP mapping to
determine the traffic class queue. By default, iSCSI flows are assigned to dot1p priority 4. To map
incoming iSCSI traffic on an interface to a dot1p priority-queue other than 4, use the CoS dot1p-
priority command (refer to QoS dot1p Traffic Classification and Queue Assignment). Dell Networking
recommends setting the CoS dot1p priority-queue to 0 (zero).
You can configure whether iSCSI frames are re-marked to contain the configured VLAN priority tag or IP
DSCP when forwarded through the switch.
NOTE: On a switch in which a large proportion of traffic is iSCSI, CoS queue assignments may
interfere with other network control-plane traffic, such as ARP or LACP. Balance preferential
treatment of iSCSI traffic against the needs of other critical data in the network.
Information Monitored in iSCSI Traffic Flows
iSCSI optimization examines the following data in packets and uses the data to track the session and
create the classifier entries that enable QoS treatment.
• Initiator’s IP Address
• Target’s IP Address
• ISID (Initiator defined session identifier)
• Initiator’s IQN (iSCSI qualified name)
• Target’s IQN
• Initiator’s TCP Port
• Target’s TCP Port
• Connection ID
• Aging
• Up Time
If no iSCSI traffic is detected for a session during a user-configurable aging period, the session data is
cleared.
If more than 256 simultaneous sessions are logged continuously, the following message displays
indicating the queue rate limit has been reached:
%STKUNIT2-M:CP %iSCSI-5-ISCSI_OPT_MAX_SESS_EXCEEDED: New iSCSI Session Ignored:
ISID -
400001370000 InitiatorName - iqn.1991-05.com.microsoft:dt-brcd-cna-2 TargetName
-
iqn.2001-05.com.equallogic:4-52aed6-b90d9446c-162466364804fa49-wj-v1 TSIH - 0"
iSCSI Optimization
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