How to Ignore the Local Disks when Generating Multipath Devices in Linux Server

Some machines have local SCSI cards for their internal disks. DM-Multipath is not recommended for these devices.

The following procedure shows how to modify the multipath  configuration file to ignore the local disks when configuring multipath.

1.  Determine which disks are the internal disks and mark them as the ones to blacklist.

In this example, /dev/sda is the internal disk. Note that as originally configured in the default multipath configuration file, executing the multipath -v2 shows the local disk, /dev/sda, in the multipath map.

[root@test ~]# multipath -v2
create: SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
[size=33 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 0:0:0:0 sda  8:0    [---------
device-mapper ioctl cmd 9 failed: Invalid argument
device-mapper ioctl cmd 14 failed: No such device or address
create: 3600a0b80001327d80000006d43621677
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:0 sdb  8:16  
  \_ 3:0:0:0 sdf  8:80  
create: 3600a0b80001327510000009a436215ec
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:1 sdc  8:32  
  \_ 3:0:0:1 sdg  8:96  
create: 3600a0b80001327d800000070436216b3
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:2 sdd  8:48  
  \_ 3:0:0:2 sdh  8:112 

2. In order to prevent the device mapper from mapping /dev/sda in its multipath maps, edit the blacklist section of the /etc/multipath.conf file to include this device. Although you could blacklist the sda device using a devnode type, that would not be safe procedure since /dev/sda is not guaranteed to be the same on reboot. To blacklist individual devices, you can blacklist using the WWID of that device.
ote that in the output to the multipath -v2 command, the WWID of the /dev/sda device is SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1.
To blacklist this device, include the following in the /etc/multipath.conf file.

blacklist {
      wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
}

3. After you have updated the /etc/multipath.conf file, you must manually tell the multipathd daemon to reload the file.

The following command reloads the updated /etc/multipath.conf file.
service multipathd reload

4. Run the following commands:

multipath -F
multipath -v2
[root@test~]# multipath -F
[root@test ~]# multipath -v2

create: 3600a0b80001327d80000006d43621677
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:0 sdb  8:16  
  \_ 3:0:0:0 sdf  8:80  
create: 3600a0b80001327510000009a436215ec
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:1 sdc  8:32  
  \_ 3:0:0:1 sdg  8:96  
create: 3600a0b80001327d800000070436216b3
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
  \_ 2:0:0:2 sdd  8:48  
  \_ 3:0:0:2 sdh  8:112