Users Guide

Configuring Multipath I/O Devices

EqualLogic Multipath I/O (MPIO) in HIT/Linux enables you to configure redundant network paths from a Linux host to PS Series volumes

for high availability and high performance SAN data traffic. MPIO accomplishes two goals:

• Creates and manages an optimal number of iSCSI sessions to each SAN volume based on the number of host NICs and the number of

group members the volume is using. HIT/Linux monitors the SAN configuration and adds sessions as the configuration changes.

• Enhances performance by directing each I/O to the proper PS Series group, reducing the amount of I/O forwarding that is necessary

between members.

This chapter describes how to use HIT/Linux to set up access to EqualLogic PS Series storage volumes, and explains how the EqualLogic

Host Connection Manager daemon (ehcmd) sets up a two-tier multipath device structure to accomplish these goals.

Topics:

• Accessing Volumes Using Multipath I/O

• Multipath Device Configuration

• Traditional Multipath Device Configurations

• Conditions for Configuring Multipath Devices

• Configuring Settings for Multipath I/O

• Including a Subnet or Adapter for MPIO

• Excluding a Subnet or Adapter From MPIO

• Including or Excluding Specific Host NICs

• Configuring I/O Path Selection

• Setting Volume-Specific Configuration Parameters

Accessing Volumes Using Multipath I/O

To access volumes using multipath I/O, you must discover targets (volumes) and then log into at least one iSCSI session to the volume.

By default, the EqualLogic Host Connection Manager (ehcmd) uses the software iSCSI initiator to connect to volumes. For information on

enabling and configuring the Broadcom iSCSI offload functionality, see Enabling iSCSI Offload on HIT/Linux.

Discovering Targets

The PS Series group address must be configured as a discovery address and a send-targets discovery executed before any volumes can

be accessed. HIT/Linux does this for you when you use the rswcli --add-group command. You can view the currently configured

discovery addresses with:

# iscsiadm -m discoverydb

Also, you can view the current list of discovered target IQN names with:

# iscsiadm -m node | sort -u

If you created additional volumes, removed volumes, or modified access to existing volumes so their visibility to the Linux host has

changed, you must run the discoverydb command to add any new volume records and remove any old volume records:

# iscsiadm -m discoverydb -p group-IP-address -t st -o new delete -D

NOTE:

Support of the iscsiadm –m discoverydb command syntax applies to systems with version 2.0-872 and later

of the iSCSI initiator tools. Earlier versions must use this syntax: iscsiadm -m discovery [-I iface ] -t st -p

group-IP-address. This command syntax will not preserve the settings in existing node records, but will reapply the

default settings specified in the iscsid.conf file. See the iscsiadm(8) manpage for more information.

30 Configuring Multipath I/O Devices