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3.2. Ignoring Local Disks when Generating Multipath Devices
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.
- Determine which disks are the internal disks and mark them as the ones to blacklist.In this example,
/dev/sdais the internal disk. Note that as originally configured in the default multipath configuration file, executing themultipath -v2shows the local disk,/dev/sda, in the multipath map.For further information on themultipathcommand output, see Section 5.1, “Multipath Command Output”.[root@rh4cluster1 ~]#
multipath -v2create: 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 create: 3600a0b80001327510000009b4362163e [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:3 sde 8:64 \_ 3:0:0:3 sdi 8:128 - In order to prevent the device mapper from mapping
/dev/sdain its multipath maps, edit thedevnode_blacklistsection of the/etc/multipath.conffile to include this device. Although you could blacklist thesdadevice using adevnodetype, that would not be safe procedure since/dev/sdais not guaranteed to be the same on reboot. To blacklist individual devices, you can blacklist using the WWID of that device.Note that in the output to themultipath -vscommand, the WWID of the/dev/sdadevice is SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1. To blacklist this device, include the following in the/etc/multipath.conffile.devnode_blacklist { wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1 } - Run the following commands:
multipath -F multipath -v2
The local disk or disks should no longer be listed in the new multipath maps, as shown in the following example.[root@rh4cluster1 ~]#
multipath -F[root@rh4cluster1 ~]#multipath -v2create: 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 create: 3600a0b80001327510000009b4362163e [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:3 sde 8:64 \_ 3:0:0:3 sdi 8:128
