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DM-Multipath configuration

You can configure DM-Multipath for use in multipathing in environments that use native Linux solutions. With DM-Multipath, you can configure multiple I/O paths between a host and storage controllers into a single device. If one path fails, DM-Multipath reroutes I/Os to the remaining paths.

Note: If you are running Veritas Storage Foundation, you need to use VxDMP as your multipathing solution.

When you have multiple paths to a LUN, Linux creates a SCSI device for each path. This means that a single LUN might appear as/dev/sdd and /dev/sdf if there are two paths to it. To make it easy to keep track of the LUNs, DM-Multipath creates a single device in /dev/mapper/ for each LUN that includes all the paths. For example, /dev/mapper/360a9800043346852563444717a513571 is the multipath device that is created on top of /dev/sdd and /dev/sdf.

When you are using DM-Multipath, you should create a file system for each LUN and then mount the LUN using the device in /dev/mapper/.

Note: To create a file system on a LUN, use /dev/mapper/device on a Linux host console.

device is the multipath device name of the LUN in the /dev/mpath/ directory.

You also use the DM-Multipath's configuration file to specify whether ALUA is being used and if the hardware handler should be enabled for ALUA.

When DM-Multipath is running, it automatically checks the paths. As a result, if you look at the output of a command such as lun stats -o, you see a small amount of FC partner path traffic listed under the operations per second. On average, this is usually about 4 kb of operations per path per LUN every 20 seconds, which is the default time period. This is expected behavior for DM-Multipath.