Configuring priority flow control for iSCSI

You can prioritize iSCSI data over other data on the network. You can also set bandwidth limits to ensure QoS to iSCSI traffic by using the Enhanced Transmission Selection (ETS) setting on the network. When you plan to configure priority flow control (PFC) for iSCSI-attached hosts, follow these guidelines and examples.

About this task

Note: PFC for iSCSI is supported on Brocade VDX 10-gigabit Ethernet switches only.

PFC (IEEE standard 802.1Qbb), is a link-level flow control mechanism. The flow control mechanism is similar to IEEE 802.3x Ethernet PAUSE. However, PFC operates on individual priorities. Instead of pausing all traffic on a link, you can selectively pause traffic according to its class.

PFC can help network congestion scenarios by pushing back on entities that are generating more traffic on the network than the network can handle. PFC cannot be enabled for IP replication traffic and system management traffic. If the same IP address is used to transmit both iSCSI and IP replication traffic, PFC is enabled for iSCSI traffic only.

To use PFC, your system must meet the following requirements:
  • PFC is supported only with ports that have 10 Gb or higher bandwidth.
  • PFC cannot be manually turned on or off from the system. PFC is automatically turned on if it is configured on the switch (network).
  • PFC is enabled only for those IP addresses where VLAN tagging is enabled on the system.
  • To enable PFC on an IP address, follow these general steps:
    1. Set the host flag to yes for that IP.
    2. Set a VLAN ID for that IP.
    3. On the switch, set the priority tag for iSCSI.
    4. On the switch, enable the PFC for iSCSI priority tag.
    5. On the switch, enable DCBX.

    For PFC to be effective for both read and write traffic from hosts, PFC must be enabled on the hosts. For information about how to turn on PFC for a host operating system, see the product documentation that is specific to that operating system.

Example

To configure iSCSI IP of type IPv4 with a VLAN ID, enter the following command:
cfgportip -node node_name | node_id -ip ipv4addr 
-gw ipv4gw -mask subnet_mask -vlan vlan_id port_id
To configure iSCSI IP of type IPv6 with a VLAN ID, enter the following command:
cfgportip -node node_name | node_id -ip_6 ipv6addr
-gw_6 ipv6gw -prefix_6 prefix -vlan_6 vlan_id |-novlan_6  port_id
To set the host flag to yes for iSCSI IP of type IPv4, enter the following command:
cfgportip -node node_name | node_id –host yes port_id
To set the host flag to yes for iSCSI IP of type IPv6, enter the following command:
cfgportip -node node_name | node_id –host_6 yes port_id
To set the VLAN ID for iSCSI IP of type IPv4, enter the following command:
cfgportip -node node_name | node_id –vlan vlan_id port_id
To set the VLAN ID for iSCSI IP of type IPv6, enter the following command:
cfgportip -node node_name | node_id –vlan_6 vlan_id port_id
Note: When you configure an iSCSI IP address, the host flag is set by default.