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How to Prepare An EXOS Switch Optimally For iSCSI Traffic

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TitleHow to Prepare An EXOS Switch Optimally For iSCSI Traffic
To prepare an EXOS switch optimally for iSCSI
  • EXOS All
  • All EXOS platforms
iSCSI is a protocol which purpose is to interconnect SCSI devices via IP networks.
To operate properly it puts some requirements on network where it is running, such as:
  • lossless packet forwarding
  • in order delivery
  • low latency

There are several recommendations which you can follow to improve iSCSI traffic forwarding.
  • Avoid packet fragmenting by enabling jumbo-frames on ports where iSCSI traffic is expected:
# enable jumbo-frame ports <PORT_LIST>
Note: please make sure that jumbo-frame settings on corresponding port match to what is configured locally.
  • Decrease latency by changing packet forwarding mode to "cut through":
# configure forwarding switching-mode cut-through
Note: please note that changing forwarding mode to cut through has several drawbacks such as:
  • FCS (frame check sequence) field in Ethernet frame is not inspected hence corrupted packets will not be detected but will be forwarded further
  • Packet buffers almost not used in "cut through" mode hence even if latency decreased, possibility of packet drop is increased in case of ports congestion
  • Some features like ACL meters don't work in "cut through" mode:
    ACL meter doesn't work in cut-through switching mode.
  • Enable PFC (Priority-Based Flow Control) for iSCSI traffic:
  1. First map such traffic to custom qos-profile:
    Configuring QOS profiles and verify QOS is working on EXOS
  2. Then enable Per-Priority PAUSE for this qos-profile. When a host receives a PAUSE frame (802.3x) all traffic ceases on the link. Per-Priority Pause frames allows specific types of traffic to be delayed (at the host) while others are allowed to flow ( traffic can be paused while regular data traffic moves along).
    # enable flow-control rx-pause qosprofile <QOS-PROFILE> ports <PORT_LIST>
    # enable flow-control tx-pause priority <PRIORITY> ports <PORT_LIST>
Additional notes



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