(MPIO) Multi-path on RHEL

Multipath on RHEL is not to difficult.

If you not sure if Multi-Path has been enabled on a server the quick and best way to o check is is via the multipath cmd.

  • # multipath -l
    mpath1 (3600d0230003228bc000339414edb8101)
    [size=10 GB][features="0"][hwhandler="0"]
    \_ round-robin 0 [prio=1][active]
     \_ 2:0:0:6 sdb 8:16 [active][ready]
    \_ round-robin 0 [prio=1][enabled]
     \_ 3:0:0:6 sdc 8:64 [active][ready]
  • -l displays in addition to all other available components of the system
  • -ll option displays the information

If you don’t get a reply from multipath cmd as in the above example. It could mean  that you need to enable Multipath. but for trying to enable it, make sure you have the hardware capability

{Useful multipath Command Options

Option Description
-l Display the current multipath configuration gathered from sysfs and the device mapper.
-ll Display the current multipath configuration gathered from sysfs, the device mapper, and all other available components on the system.
-f device Remove the named multipath device.
-F Remove all unused multipath devices.

}

Determining Device Mapper Entries with the dmsetup Command

You can use the dmsetup command to find out which device mapper entries match the multipathed devices.
The following command displays all the device mapper devices and their major and minor numbers. The minor numbers determine the name of the dm device. For example, a minor number of 3 corresponds to the multipathed device /dev/dm-3.
# dmsetup ls
mpath2  (253, 4)
mpath4p1        (253, 12)
mpath5p1        (253, 11)
mpath1  (253, 3)
mpath6p1        (253, 14)
mpath7p1        (253, 13)
mpath0  (253, 2)
mpath7  (253, 9)
mpath6  (253, 8)
VolGroup00-LogVol01     (253, 1)
mpath5  (253, 7)
VolGroup00-LogVol00     (253, 0)
mpath4  (253, 6)
mpath1p1        (253, 10)
mpath3  (253, 5)

Troubleshooting with the multipathd Interactive Console

The multipathd -k command is an interactive interface to the multipathd daemon. Entering this command brings up an interactive multipath console. After entering this command, you can enter help to get a list of available commands, you can enter a interactive command, or you can enter CTRL-D to quit.
The multipathd interactive console can be used to troubleshoot problems you may be having with your system. For example, the following command sequence displays the multipath configuration, including the defaults, before exiting the console.
# multipathd -k
> > show config
> > CTRL-D
The following command sequence ensures that multipath has picked up any changes to the multipath.conf,
# multipathd -k
> > reconfigure
> > CTRL-D

Use the following command sequence to ensure that the path checker is working properly.

# multipathd -k
> > show paths
> > CTRL-D

 

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