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Dell Configuration Guide for the S4048–ON System 9.14.2.6

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iSCSI Optimization Overview

iSCSI is a TCP/IP-based protocol for establishing and managing connections between IP-based storage devices and initiators in a storage area network (SAN).

iSCSI optimization enables the network switch to auto-detect Dell’s iSCSI storage arrays and triggers a self-configuration of several key network configurations that enables optimization of the network for better storage traffic throughput. iSCSI is disabled by default.

iSCSI optimization also provides a means of monitoring iSCSI sessions and applying quality of service (QoS) policies on iSCSI traffic. When enabled, iSCSI optimization allows a switch to monitor (snoop) the establishment and termination of iSCSI connections. The switch uses the snooped information to detect iSCSI sessions and connections established through the switch.

iSCSI optimization allows you to reduce deployment time and management complexity in data centers. In a data center network, Dell EqualLogic and Compellent iSCSI storage arrays are connected to a converged Ethernet network using the data center bridging exchange protocol (DCBx) through stacked and/or non-stacked Ethernet switches.

iSCSI session monitoring over virtual link trunking (VLT) synchronizes the iSCSI session information between the VLT peers, allowing session information to be available in both the VLT peers. You can enable or disable iSCSI when you configure VLT.

iSCSI optimization functions as follows:
  • Auto-detection of EqualLogic storage arrays — the switch detects any active EqualLogic array directly attached to its ports.
  • Manual configuration to detect Compellent storage arrays where auto-detection is not supported.
  • Automatic configuration of switch ports after detection of storage arrays.
  • If you configure flow-control, iSCSI uses the current configuration. If you do not configure flow-control, iSCSI auto-configures flow control settings so that receive-only is enabled and transmit-only is disabled. .
  • iSCSI monitoring sessions — the switch monitors and tracks active iSCSI sessions in connections on the switch, including port information and iSCSI session information.
  • iSCSI QoS — A user-configured iSCSI class of service (CoS) profile is applied to all iSCSI traffic. Classifier rules are used to direct the iSCSI data traffic to queues that can be given preferential QoS treatment over other data passing through the switch. Preferential treatment helps to avoid session interruptions during times of congestion that would otherwise cause dropped iSCSI packets.
  • iSCSI DCBx TLVs are supported.
NOTE After a switch is reloaded, powercycled, or upgraded, any information exchanged during the initial handshake is not available. If the switch establishes communication after reloading, it detects that a session was in progress but could not obtain complete information for it. Any incomplete information is not available in the show commands.
NOTE After a switch is reloaded, powercycled, or upgraded, the system may display the ACL_AGENT-3-ISCSI_OPT_MAX_SESS_LIMIT_REACHED: Monitored iSCSI sessions reached maximum limit log message. This cannot be inferred as the maximum supported iSCSI sessions are reached. Also, number of iSCSI sessions displayed on the system may show any number equal to or less than the maximum.

The following illustration shows iSCSI optimization between servers and a storage array in which a stack of three switches connect installed servers (iSCSI initiators) to a storage array (iSCSI targets) in a SAN network. iSCSI optimization running on the master switch is configured to use dot1p priority-queue assignments to ensure that iSCSI traffic in these sessions receives priority treatment when forwarded on stacked switch hardware.

Figure 1. iSCSI Optimization Example
Illustration of an iSCSI optimization example.

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