Administrator Guide

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.
Detection and Auto-Configuration for Dell EqualLogic
Arrays
The iSCSI optimization feature includes auto-provisioning support with the ability to detect directly connected Dell EqualLogic storage
arrays and automatically reconfigure the switch to enhance storage traffic flows.
The switch uses the link layer discovery protocol (LLDP) to discover Dell EqualLogic devices on the network. LLDP is enabled by default.
For more information about LLDP, refer to Link Layer Discovery Protocol (LLDP).
iSCSI Optimization
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