Linux MultiPathing howto.

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Written by Syed Asim Abbas   
Monday, 26 October 2009 08:53
Linux MultiPathing Howto. By Syed Asim Abbas
Date: 24-10-2009
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Device Mapper Multipath (DM-MP) allows nodes to route I/O over multiple paths to a storage controller.
 A path refers to the  connection from an HBA port to a storage controller port. As paths
fail and new paths come up, DM-MP reroutes the I/O over the available paths.

Easy way to configure Multipathing
------------------------------------


[root@power root]# rpm -qa |grep multipath
device-mapper-multipath-0.4.8-7.fc10.i386




[root@power root]# fdisk -l

Disk /dev/sda: 60.0 GB, 60011642880 bytes
255 heads, 63 sectors/track, 7296 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x3f443f43

   Device Boot      Start         End      Blocks   Id  System


Disk /dev/sdg: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdn: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdh: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdo: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

MultiPathing packaged avilable on Distribution


###Check the SCSI IDs to see the disk are pairs. /dev/sda is my system disk so no need to configure it for multipathing. Sdg , sdn, sdh and sdo are SAN connected disks.


[root@power root]# scsi_id -g -u -s /block/sdg
360060e8005bcaf000000bcaf00006024
[root@power root]# scsi_id -g -u -s /block/sdn
360060e8005bcaf000000bcaf00006024

[root@power root]# scsi_id -g -u -s /block/sdh
360060e8005bcaf000000bcaf00005033
[root@power root]# scsi_id -g -u -s /block/sdo
360060e8005bcaf000000bcaf00005033

##Ok sdg,sdn Pair and sdh,sdo Pair .

###To implement multipath environment, you must define the alias names for the multipath devices by editing the multipath.conf file that resides in the /etc/ directory:


[root@power root]# vi /etc/multipath.conf

# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
blacklist {
        devnode "*"
}


##############Comment The above lines


# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
#blacklist {
#        devnode "*"
#}

#########Define the Disks Aliases ##########

multipaths {


 multipath {
                wwid                    360060e8005bcaf000000bcaf00006024
                alias                   ora1
        }

multipath {
                wwid                    360060e8005bcaf000000bcaf00005033
                alias                   ora2
        }

}


####### Save the configuration

[root@power root]# chkconfig multipathd on


[root@power root]# service multipathd restart
Stopping multipathd daemon:                                [FAILED]
Starting multipathd daemon:                                [  OK  ]
[root@power root]#


[root@power root]# fdisk -l

Disk /dev/sda: 60.0 GB, 60011642880 bytes
255 heads, 63 sectors/track, 7296 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x3f443f43

   Device Boot      Start         End      Blocks   Id  System


Disk /dev/sdg: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdn: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdh: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdo: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System




##########No update same result. Restart the system and run fdisk -l



[root@power root]# fdisk -l

Disk /dev/sda: 60.0 GB, 60011642880 bytes
255 heads, 63 sectors/track, 7296 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x3f443f43

   Device Boot      Start         End      Blocks   Id  System


Disk /dev/sdg: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdn: 107.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdh: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/sdo: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/dm-0: 70.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/dm-1: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System

Disk /dev/mpath/ora1: 70.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System


Disk /dev/mpath/ora2: 153.0 GB, 60011642880 bytes
Device Boot      Start         End      Blocks   Id  System


#########Ok four more disks are aviavlable. Don't confude just used your paths  /dev/mpath/ora1  /dev/mpath/ora2


[root@power root]# ls /dev/mpath*

ora1    ora2

####Disks multipath names are available now. Mount the devices using new name.



[root@power root]# mount /dev/mpath/ora1 /ora1
 
[root@power root]# mount /dev/mpath/ora2 /ora2


For testing unplugged one fiber link and see the results.
come from:http://www.wbitt.com/contributed-howtos/141-linux-multipathing-howto.html

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