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Chapter 3. Setting Up DM-Multipath

This chapter provides step-by-step example procedures for configuring DM-Multipath. It includes the

following procedures:

Basic DM-Multipath setup

Ignoring local disks

Adding more devices to the configuration file

3.1. Setting Up DM-Multipath

Before setting up DM-Multipath on your system, ensure that your system has been updated and

includes the device-mapper-m ultipath package.

Use the following procedure to set up DM-Multipath for a basic failover configuration.

1. Edit the /etc/multipath.conf file by commenting out the following lines at the top of the file.

This section of the configuration file, in its initial state, blacklists all devices. You must comment it

out to enable multipathing.

devnode_blacklist {

devnode "*"

}

After commenting out those lines, this section appears as follows.

# devnode_blacklist {

# devnode "*"

# }

2. T he default settings for DM-Multipath are compiled in to the system and do not need to be

explicitly set in the /etc/multipath.conf file.

The default value of path_grouping_policy is set to failover, so in this example you do

not need to change the default value. For information on changing the values in the configuration

file to something other than the defaults, see Chapter 4, The DM-Multipath Configuration File.

The initial defaults section of the configuration file configures your system that the names of the

multipath devices are are of the form m pathn; without this setting, the names of the multipath

devices would be aliased to the WWID of the device.

3. Save the configuration file and exit the editor.

4. Execute the following commands:

modprobe dm-multipath

service m ultipathd start

multipath -v2

The m ultipath -v2 command prints out multipathed paths that show which devices are

multipathed, but only for the devices created by this command. If the command does yield any

output, you can check your multipath devices as follows:

Run the m ultipath -ll command. This lists all the multipath devices.

If running the m ultipath -ll command does not show the device, verify that multipath is

configured properly by checking the /etc/multipath file and making sure that the SCSI

devices you want to be multipathed exist on the system.

Red Hat Enterprise Linux 4 DM Multipath

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Red Hat LINUX VIRTUAL SERVER 4.7 - ADMINISTRATION Guia de Instalação Página 17