安装与配置DM-multipath 安装运行DM软件
# yum install device-mapper-multipath
# /etc/init.d/multipathdrestart
ok
Stopping multipathddaemon: [ OK ]
Starting multipathddaemon: [ OK ]
Multipathd服务启动后，会通过SCSI ID自动寻找同一设备的多条路径，并安装缺省设置把它们聚合起来使用。
# multipath -ll
mpathb (1IET 00010001) dm-3 lb,lb_iscsi #'1IET 00010001'表示远程设备信息(CentOS6.5的DM multipath 0.4.9用它作为SCSI ID) dm-3 lb 表示厂商 lb_iscsi产品信息 这种情况就可以实现单点故障切换
size=5.0G features='0'hwhandler='0' wp=rw
|-+- policy='round-robin 0'prio=1 status=active #status=active 默认使用的链路
| `- 3:0:0:1 sdb 8:16 activeready running
`-+- policy='round-robin 0'prio=1 status=enabled #status=enabled有效链路，但是不是活动链路,备用链路
`- 4:0:0:1 sdd 8:48 active ready running
配置multipath
2.1修改文件/etc/multipath.conf
默认情况下/etc目录下没有配置文件multipath.conf的。需要从/usr/share/doc/目录下拷贝过来使用。
#cp/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf /etc/
可以用man multipath.conf命令或者查看文件/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.annotated了解配置选项的解释。
在此，通过在文件中加入下列配置行，我们为SCSI ID为"1IET 00010001"的设备设置了round-robin负载均衡模式（缺省是active-standby模式）
multipaths {
multipath {
wwid "1IET 00010001"
alias yellow
path_grouping_policy multibus
path_selector "round-robin 0"
failback manual
rr_weight priorities
no_path_retry 5
}
2.2重启multipathd服务，让修改生效
# /etc/init.d/multipathdrestart
# /etc/init.d/iscsirestart #实战发现必须做这一步，否则有问题，原因待查
验证multpath配置# multipath -ll
yellow (1IET 00010001) dm-2 lb,lb_iscsi
size=10G features='1queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0'prio=1 status=active
|- 6:0:0:1 sdc 8:32 active ready running #在此可以看到设备都是active状态
`- 5:0:0:1 sdb 8:16 active ready running #在此可以看到设备都是active状态
模拟网卡故障，验证multipath的failover功能# ifdown eth2 #执行后需要等几秒让DM确认该IP路径down掉
Device state: 3(disconnected)
# multipath -ll
Mar 23 17:12:21 |/etc/multipath.conf line 67, invalid keyword: path_checker
yellow (1IET 00010001) dm-2 lb,lb_iscsi
size=10G features='1queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1status=active
|- 7:0:0:1 sdd 8:48 active faulty running
`- 8:0:0:1 sdc 8:32 active ready running
# ifup eth2
Active connection state:activated
Active connection path:/org/freedesktop/NetworkManager/ActiveConnection/3
# multipath -ll
Mar 23 17:15:43 |/etc/multipath.conf line 67, invalid keyword: path_checker
yellow (1IET 00010001) dm-2 lb,lb_iscsi
size=10G features='1queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0'prio=1 status=active
|- 7:0:0:1 sdd 8:48 failed ready running
`- 8:0:0:1 sdc 8:32 active ready running
# sleep 60 #等待60秒
# multipath –ll #此时路径恢复
Mar 23 17:17:05 |/etc/multipath.conf line 67, invalid keyword: path_checker
yellow (1IET 00010001) dm-2 lb,lb_iscsi
size=10G features='1 queue_if_no_path'hwhandler='0' wp=rw
`-+- policy='round-robin 0'prio=1 status=active
|- 7:0:0:1 sdd 8:48 active ready running
`- 8:0:0:1 sdc 8:32 active readyrunning