How To's Tutorials
DM-Multipath stands for Device mapper multipathing. It allows us to configure multiple I/O paths between server and storage arrays into a single device. These I/O paths are physical SAN connections that can include separate cables, switches, and controllers.
Multipathing aggregates the I/O paths, creating a new device that consists of the aggregated paths and remove the Single Point of Failure Problem.
Below are the two reasons why we are using DM-Multipath on Linux Servers :
Redundancy : In Case of active/passive multipathing we will be using two paths. One path will be used for I/O operations and other will be in stand by. If any element of an I/O path (like cable, switch, or controller) fails, DM-Multipath switches to an alternate path or stand by path.
High Performance : In case of active/active multipathing , I/O operations are shared over available paths in round-robin fashion and provide improved performance.
‘device-mapper-multipath’ is the multipath rpm package
# rpm -q device-mapper-multipath
if it is not installed then use the below yum command :
# yum install device-mapper-multipath
‘/etc/multipath.conf’ is the default configuration file for multipathing , if this file doesn’t exists , copy the sample file :
# cp /usr/share/doc/device-mapper-multipath-<version>/multipath.conf /etc
Now Edit the file /etc/multipath.conf and make sure following line exists and commented out:
Above Section of multipath.conf file blacklists all the devices by default. We must comment it out to enable multipathing.
Multipath is controlled by the multipathd service
# service multipathd start ; chkconfig multipathd on
# multipath -v2
“ multipath -v2” command scans, identifies, and configures multipath maps for devices that could have multiple paths to storage, as configured in /etc/multipath.conf
To display the multipath :
# multipath –ll
Note : In Case Sample file doesn’t exist on above path, then we can use mpathconf utility which will create /etc/multipath.conf file from scratch.
To Enable Basic multipathing failover :
# mpathconf --enable --with_multipathd y
Now enable multipath, allow it to use user_friendly_names, as well as to find_multipaths
# mpathconf --enable --user_friendly_names y --find_multipaths y
Restart the Service
# service multipathd restart
Configure VSFTPD Chroot