Configuring Path Failover Policies And Priorities; Configuring The Path Failover Policies; Configuring Failover Priorities - Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

7.6 Configuring Path Failover Policies and
Priorities
In a Linux host, when there are multiple paths to a storage controller, each path appears as a separate
block device, and results in multiple block devices for single LUN. The Device Mapper Multipath
service detects multiple paths with the same LUN ID, and creates a new multipath device with that
ID. For example, a host with two HBAs attached to a storage controller with two ports via a single
unzoned Fibre Channel switch sees four block devices:
. The Device Mapper Multipath service creates a single block device,
dev/sdd
that reroutes I/O through those four underlying block devices.
mpath1
This section describes how to specify policies for failover and configure priorities for the paths.
Section 7.6.1, "Configuring the Path Failover Policies," on page 61
Section 7.6.2, "Configuring Failover Priorities," on page 61
Section 7.6.3, "Using a Script to Set Path Priorities," on page 67
Section 7.6.4, "Configuring ALUA," on page 67
Section 7.6.5, "Reporting Target Path Groups," on page 69

7.6.1 Configuring the Path Failover Policies

Use the command with the -p option to set the path failover policy:
multipath
multipath devicename -p policy
Replace policy with one of the following policy options:
Group Policy Options for the multipath -p Command
Table 7-4
Policy Option Description
failover One path per priority group.
multibus All paths in one priority group.
group_by_serial One priority group per detected serial number.
group_by_prio One priority group per path priority value. Priorities are determined by callout
programs specified as a global, per-controller, or per-multipath option in the
etc/multipath.conf
group_by_node_name One priority group per target node name. Target node names are fetched in the
/sys/class/fc_transport/target*/node_name

7.6.2 Configuring Failover Priorities

You must manually enter the failover priorities for the device in the
Examples for all settings and options can be found in the
multipath-tools/multipath.conf.annotated
"Understanding Priority Groups and Attributes" on page 62
"Configuring for Round-Robin Load Balancing" on page 66
,
/dev/sda /dev/sdb
configuration file.
/etc/multipath.conf
/usr/share/doc/packages/
file.
Managing Multipath I/O for Devices
, , and
/dev/sdc /
/dev/mpath/
/
location.
file.
61