Administrator Guide

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 QoS dot1p-priority command (refer to QoS dot1p Traffic Classification and Queue
Assignment). Dell EMC 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"
NOTE:
If you are using EqualLogic or Compellent storage arrays, more than 256 simultaneous iSCSI sessions are possible.
However, iSCSI session monitoring is not capable of monitoring more than 256 simultaneous iSCSI sessions. If this number
is exceeded, sessions may display as unknown in session monitoring output. Dell EMC Networking recommends that you
disable iSCSI session monitoring for EqualLogic and Compellent storage arrays or for installations with more than 256
simultaneous iSCSI sessions.
Only sessions the switch observes are learned; sessions flowing through an adjacent switch are not learned. Session monitoring
learns sessions that actually flow through the switch, it does not learn all sessions in the entire topology.
After a switch is reloaded, any information exchanged during the initial handshake is not available. If the switch picks up the
communication after reloading, it would detect a session was in progress but could not obtain complete information for it. Any
incomplete information of this type would not be available in the show commands.
iSCSI Optimization
451