Multipathing in Linux

Multipathing is used for Load Balancing, path failover & Recover for block devices in Linux.

Load balancing:

The workload is distributed across the available hardware components.

Path failover & Recover:

Will use redundant I/O channels to redirect the read and write operations when one or more paths no longer available.

Prerequisites RPM’s:

1. device-mapper-1.02.77-9.el6.x86_64
2. device-mapper-multipath-libs-0.4.9-64.0.1.el6.x86_64
3. device-mapper-multipath-0.4.9-64.0.1.el6.x86_64

Daemon: Multipathd

Configuration file: /etc/multipath.conf

The “multipath.conf” has five sections:

1. System level defaults
2. Blacklisted devices
3. Blacklist exceptions
4. Storage controller specific settings
5. Device specific settings

Simple steps to configure multipath:

1. For configuring the Multipath in Redhat Linux, device-mapper-multipath should be installed. You can verify It by using below command that it is installed or not:

#rpm -q device-mapper*

2. If it is not installed, install it by using below command.

#yum install device-mapper

3. After installation, start to configure multipath

#cd /etc

#mv multipath.conf multipath.conf.dist

#sed ‘/^#/d; /^$/d’ multipath.conf.dist > multipath.conf

#vi multipath.conf

Change to blacklist local hard drive only,

blacklist {
devnode “sda”
}

4. Now start the Multipath service

#Service Multipathd start
#chkconfig Multipathd on

5. Now Verify the disk paths

#fdisk -l
#sfdisk –s

Commands:

#service Multipathd start – to start the multipath service

#service Multipathd stop – to stop the multipath service

#service Multipathd reload – To update the modified configurations to replicate without restarting the service.

#multipath –ll – To list all the multipathed devices

#multipath –F – to stop the multipath