device mapper multipath

Device mapper multipath .

Guys, it is true from my heart that understanding a multipath solution ( especially device-mapper-multipath) is a simple process.

I am more familiar with the multipath solution “device-mapper-multipath” which shipped with the #1 enterprise release RHEL ( Red Hat Enterprise Linux ) .

The mulitpath solution is achieved with the kernel module called “dm_multipath”.

[root@dhcp209-115 ~]# lsmod |grep dm_multipath
dm_multipath 56921 3 dm_emc,dm_round_robin
dm_mod 101905 33 dm_snapshot,dm_multipath
scsi_dh 42177 2 dm_multipath,scsi_dh_rdac
[root@dhcp209-115 ~]#

The related package is “device-mapper-multipath”……..

[root@dhcp209-115 ~]# rpm -q device-mapper-multipath
device-mapper-multipath-0.4.7-34.el5
[root@dhcp209-115 ~]#

How to configure multipath in a system is a simple task .. I would recommend you to refer below kbase for the same.

kbase.redhat.com/faq/docs/DOC-3691

I know it is written for RHEL 4, but it works the same way in RHEL 5 🙂

If you have properly configured multipath, an output similar to below will be provided for the command “multipath -ll”.

[root@dhcp209-115 ~]# multipath -ll
mpath0 (1IET_00010001) dm-2 DGC,RAID 5
[size=200.0G][features=1 queue_if_no_path][hwhandler=1 emc][rw]
\_ round-robin 0 [prio=1][active]
\_ 2:0:0:1 sda 8:0 [active][ready]
\_ round-robin 0 [prio=0][enabled]
\_ 3:0:0:1 sdb 8:16 [active][ready]
[root@dhcp209-115 ~]#

I am bit lazy to explain above output as it is already documented here..

sources.redhat.com/lvm2/wiki/MultipathUsageGuide

For an end user the above information is sufficient to grasp the technology and for the desired result.. 🙂

I will come up with internals of the same in some other blog ..

References:

www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.5/html/DM_Multipath/index.html