Configuring Path Failover Policies And Priorities; Configuring The Path Failover Policies; Configuring Failover Priorities - Novell LINUX ENTERPRISE SERVER 10 SP3 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

5.6 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 5.6.1, "Configuring the Path Failover Policies," on page 60
Section 5.6.2, "Configuring Failover Priorities," on page 60
Section 5.6.3, "Using a Script to Set Path Priorities," on page 65
Section 5.6.4, "Configuring ALUA," on page 65
Section 5.6.5, "Reporting Target Path Groups," on page 67

5.6.1 Configuring the Path Failover Policies

Use the
multipath
multipath devicename -p policy
Replace policy with one of the following policy options:
Group Policy Options for the multipath -p Command
Table 5-4
Policy Option
failover
multibus
group_by_serial
group_by_prio
group_by_node_name

5.6.2 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 61
"Configuring for Round-Robin Load Balancing" on page 64
60 SLES 10 SP3: Storage Administration Guide
command with the -p option to set the path failover policy:
Description
One path per priority group.
All paths in one priority group.
One priority group per detected serial number.
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
One priority group per target node name. Target node names are fetched in the
/sys/class/fc_transport/target*/node_name
,
/dev/sda /dev/sdb
configuration file.
/etc/multipath.conf
/usr/share/doc/packages/
file.
, , and
/dev/sdc /
/dev/mpath/
/
location.
file.