Users Guide

Application of Quality of Service to iSCSI Trac Flows
You can congure iSCSI CoS mode. This mode controls whether CoS (dot1p priority) queue assignment and/or packet marking is
performed on iSCSI trac.
When you enable iSCSI CoS mode, the CoS policy is applied to iSCSI trac. 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 trac.
You can congure whether the iSCSI optimization feature uses the VLAN priority or IP DSCP mapping to determine the trac class queue.
By default, iSCSI ows are assigned to dot1p priority 4. To map incoming iSCSI trac on an interface to a dot1p priority-queue other than 4,
use the QoS dot1p-priority command (refer to QoS dot1p Trac Classication and Queue Assignment). Dell Networking
recommends setting the CoS dot1p priority-queue to 0 (zero).
You can congure whether iSCSI frames are re-marked to contain the congured VLAN priority tag or IP DSCP when forwarded through
the switch.
NOTE: On a switch in which a large proportion of trac is iSCSI, CoS queue assignments may interfere with other network
control-plane trac, such as ARP or LACP. Balance preferential treatment of iSCSI trac against the needs of other critical data
in the network.
Information Monitored in iSCSI Trac Flows
iSCSI optimization examines the following data in packets and uses the data to track the session and create the classier entries that
enable QoS treatment.
• Initiator’s IP Address
• Target’s IP Address
• ISID (Initiator dened session identier)
• Initiator’s IQN (iSCSI qualied name)
• Target’s IQN
• Initiator’s TCP Port
• Target’s TCP Port
• Connection ID
• Aging
• Up Time
If no iSCSI trac is detected for a session during a user-congurable 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 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 owing through an adjacent switch are not learned. Session monitoring learns
sessions that actually ow through the switch, it does not learn all sessions in the entire topology.
iSCSI Optimization
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