Используется для повышения отказоустойчивости и распределения нагрузки.

В Linux реализован при помощи специального драйвера device-mapper'а.

Cek HBA WWN nya
# cat /proc/scsi/qla2xxx/2 |grep port
scsi-qla1-adapter-port=210000145e24e4d5;
# cat /proc/scsi/qla2xxx/1 |grep port
scsi-qla0-adapter-port=210000145e24e4d4;

Cek Aplikasi Device mapper & Installasi
# rpm -qa|grep device-mapper

# wget ftp://ftp.pbone.net/mirror/ftp.centos.org/4.6/os/i386/
CentOS/RPMS/device-mapper-multipath-0.4.5-27.RHEL4.i386.rpm

# wget ftp://ftp.pbone.net/mirror/ftp.centos.org/4.6/os/i386/
CentOS/RPMS/sysfsutils-1.2.0-1.i386.rpm
# rpm -ivh sysfsutils-1.2.0-1.i386.rpm
# rpm -ivh device-mapper-multipath-0.4.5-27.RHEL4.i386.rpm

ModProbe ke Kernel
# modprobe dm-multipath

Startup Config
# chkconfig multipathd on
# service multipathd start

Inisialisasi Multipathing untuk Pertama Kali
# dmsetup ls --target=multipath
360060e80042ab00000002ab00000010b (253, 0)

Cek Multipathingnya
# multipath -ll
360060e80042ab00000002ab00000010b
[size=50 GB][features=”0″][hwhandler=”0″]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 2:0:0:0 sdc 8:32 [active][ready]

Verifikasi
# scsi_id -g -s /block/sdb
360060e80042ab00000002ab00000010b
# scsi_id -g -s /block/sdc
360060e80042ab00000002ab00000010b

'''!!!Внимание''' для последних версий изменился синтаксис команды scsi_id, теперь нужно писать
# scsi_id -g -d /dev/sdb
и
# scsi_id -g -d /dev/sdс

Edit Konfigurasi, Untuk menambahkan device yang akan di”black list” dari multipathing,
penggunaan “Friendly Name”, di Multipathnya
# vi /etc/multipath.conf

————-add config—————–
# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
devnode_blacklist {
devnode cciss
devnode fd
devnode hd
devnode md
devnode sr
devnode scd
devnode st
devnode ram
devnode raw
devnode loop
devnode sda # internal disk saya
}

## Use user friendly names, instead of using WWIDs as names.
defaults {
user_friendly_names yes
path_grouping_policy multibus
failback immediate
}
—————end config—————–

Simpan Konfigurasinya
# multipath -F

Cek Disknya
# multipath -v2
create: mpath0 (360060e80042ab00000002ab00000010b)
[size=50 GB][features=”0″][hwhandler=”0″]
\_ round-robin 0 [prio=1]
\_ 1:0:0:0 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1]
\_ 2:0:0:0 sdc 8:32 [active][ready]

Cek “friendly namesnya” sudah jalan Pa belum
# multipath -ll
mpath0 (360060e80042ab00000002ab00000010b)
[size=50 GB][features=”0″][hwhandler=”0″]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 2:0:0:0 sdc 8:32 [active][ready]

Tambahkan Nama devices ke database Multipath
# multipath -v3|egrep "vendor|product"
vendor = HITACHI
product = OPEN-V
vendor = HITACHI
product = OPEN-V

# vi /etc/multipath.conf

——–add config———
devices {
device {
vendor “HITACHI”
product “OPEN-V.”
getuid_callout “/sbin/scsi_id -g -u -p0×80 -s /block/%n”
}
}
———end config——–

# multipath -F
# multipath -ll
mpath0 (SHITACHI_OPEN-V_________10928_)
[size=50 GB][features=”0″][hwhandler=”0″]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 2:0:0:0 sdc 8:32 [active][ready]

Bikin Mount Point Baru
# fdisk -l /dev/mapper/mpath0

Disk /dev/mapper/mpath0: 53.6 GB, 53688664064 bytes
64 heads, 32 sectors/track, 51201 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes

# pvcreate /dev/mapper/mpath0
Physical volume “/dev/mapper/mpath0″ successfully created

# vgcreate vg00 /dev/mapper/mpath0
Volume group “vg00″ successfully created

# lvcreate -L 25G -n lvol1 vg00
Logical volume “lvol1″ created

# mkfs.ext3 /dev/vg00/lvol1
# mkdir /archive
# mount /dev/vg00/lvol1 /archive
# vi /etc/fstab

——–add config———
/dev/mapper/vg00-lvol1 /archive ext3 defaults 1 2
——–end config———

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 20G 9.2G 9.2G 50% /
/dev/sda1 190M 18M 163M 10% /boot
none 2.0G 0 2.0G 0% /dev/shm
/dev/sda6 15G 4.7G 9.0G 35% /home
/dev/sda7 9.7G 56M 9.1G 1% /opt
/dev/sda8 3.9G 59M 3.6G 2% /tmp
/dev/sda5 15G 7.2G 6.6G 53% /var
/dev/mapper/vg00-lvol1 25G 77M 24G 1% /archive

Extend MountPoint Barunya
# lvdisplay /dev/vg00/lvol1

— Logical volume —
LV Name /dev/vg00/lvol1
VG Name vg00
LV UUID uRNOWC-2OQ8-SNSD-BgB1-3i1y-eYVe-21Y11n
LV Write Access read/write
LV Status available
# open 1
LV Size 35.00 GB
Current LE 8960
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:1

# lvextend -L +10G /dev/vg00/lvol1
Extending logical volume lvol1 to 35.00 GB
Logical volume lvol1 successfully resized

# ext2online /archive
ext2online v1.1.18 - 2001/03/18 for EXT2FS 0.5b

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 20G 9.2G 9.2G 50% /
/dev/sda1 190M 18M 163M 10% /boot
none 2.0G 0 2.0G 0% /dev/shm
/dev/sda6 15G 4.7G 9.0G 35% /home
/dev/sda7 9.7G 56M 9.1G 1% /opt
/dev/sda8 3.9G 59M 3.6G 2% /tmp
/dev/sda5 15G 7.2G 6.6G 53% /var
/dev/mapper/vg00-lvol1 35G 81M 33G 1% /archive

Источник: http://xgu.ru/wiki/Multipath