Linux Multipath多路径配置与使用案例

本文源自：http://blog.itpub.net/31015730/viewspace-2146732/

在Linux平台一部分存储产品使用操作系统自带的多路径软件，包括最常见的HP和IBM的部分存储产品，在Linux自带的多路径软件叫做multipath，这篇文章以HP EVA系列存储在Linux平台的使用为例，详细的在Linux平台配置和使用多路径。

那么问题就来了，到底什么是多路径？

普通的电脑主机都是一个硬盘挂接到一个总线上，这里是一对一的关系。而到了有光纤组成的SAN环境，或者由iSCSI组成的IPSAN环境，由于主机和存储通过了光纤交换机或者多块网卡及IP来连接，这样的话，就构成了多对多的关系。也就是说，主机到存储可以有多条路径可以选择。主机到存储之间的IO由多条路径可以选择。每个主机到所对应的存储可以经过几条不同的路径，如果是同时使用的话，I/O流量如何分配？其中一条路径坏掉了，如何处理？从在操作系统的角度来看，每条路径，操作系统会认为是一个实际存在的物理盘，但实际上只是通向同一个物理盘的不同路径而已，这样是在使用的时候，就给用户带来了困惑。多路径软件就是为了解决上面的问题应运而生的。

多路径的主要功能就是和存储设备一起配合实现如下功能：
1、故障的切换和恢复
2、IO流量的负载均衡
3、磁盘的虚拟化

由于多路径软件是需要和存储在一起配合使用的，不同的厂商基于不同的操作系统，都提供了不同的版本。并且有的厂商，软件和硬件也不是一起卖的，如果要使用多路径软件的话，可能还需要向厂商购买license才行。比如EMC公司基于linux下的多路径软件，就需要单独的购买license。好在， RedHat和Suse的2.6的内核中都自带了免费的多路径软件包，并且可以免费使用，同时也是一个比较通用的包，可以支持大多数存储厂商的设备，即使是一些不是出名的厂商，通过对配置文件进行稍作修改，也是可以支持并运行的很好的。

一、Linux下multipath介绍

在redhat中，安装操作系统的时候multipath已经默认被安装，查看安装情况：

[root@seaing ~]# rpm -qa | grep device-mapper

device-mapper-multipath-0.4.7-34.el5

device-mapper-1.02.39-1.el5

device-mapper-event-1.02.39-1.el5

1、device-mapper-multipath：即multipath-tools。主要提供multipathd和multipath等工具和 multipath.conf等配置文件。这些工具通过device mapper的ioctr的接口创建和配置multipath设备（调用device-mapper的用户空间库。创建的多路径设备会在/dev /mapper中）。

2、 device-mapper：主要包括两大部分：内核部分和用户部分。内核部分主要由device mapper核心（dm.ko）和一些target driver（md-multipath.ko）。核心完成设备的映射，而target根据映射关系和自身特点具体处理从mappered device 下来的i/o。同时，在核心部分，提供了一个接口，用户通过ioctr可和内核部分通信，以指导内核驱动的行为，比如如何创建mappered device，这些divece的属性等。linux device mapper的用户空间部分主要包括device-mapper这个包。其中包括dmsetup工具和一些帮助创建和配置mappered device的库。这些库主要抽象，封装了与ioctr通信的接口，以便方便创建和配置mappered device。multipath-tool的程序中就需要调用这些库。

3、dm-multipath.ko和dm.ko：dm.ko是device mapper驱动。它是实现multipath的基础。dm-multipath其实是dm的一个target驱动。

4、scsi_id：包含在udev程序包中，可以在multipath.conf中配置该程序来获取scsi设备的序号。通过序号，便可以判断多个路径对应了同一设备。这个是多路径实现的关键。scsi_id是通过sg驱动，向设备发送EVPD page80或page83 的inquery命令来查询scsi设备的标识。但一些设备并不支持EVPD 的inquery命令，所以他们无法被用来生成multipath设备。但可以改写scsi_id，为不能提供scsi设备标识的设备虚拟一个标识符，并输出到标准输出。multipath程序在创建multipath设备时，会调用scsi_id，从其标准输出中获得该设备的scsi id。在改写时，需要修改scsi_id程序的返回值为0。因为在multipath程序中，会检查该直来确定scsi id是否已经成功得到。

想了解更多关于Device Mapper Multipath（DM-Multipath），请参考博文：http://blog.csdn.net/holandstone/article/details/7050234

二、Linux下multipath详细配置

首先，我们本次Linux下multipath的整体的拓扑结构，如下所示：

因为在安装操作系统的时候，multipath的软件包已经那装好了，所以这里就不在需要安装，如果没有安装的话，需要手动的进行安装。

1、检查安装是否正常

[root@seaing ~]# lsmod |grep dm_multipath

dm_multipath 56921 2 dm_round_robin

scsi_dh 42177 1 dm_multipath

dm_mod 101649 19 dm_multipath,dm_raid45,dm_snapshot,dm_zero,dm_mirror,dm_log

如果模块没有加载成功，请使用下面的命令初始化DM：

[root@seaing ~]#modprobe dm-multipath
[root@seaing ~]#modprobe dm-round-robin
[root@seaing ~]#service multipathd start
[root@seaing ~]#multipath –v2

2、编辑配置文件

[root@seaing ~]# cat /etc/multipath.conf

blacklist {

devnode "^sda"

}

defaults {

user_friendly_names no

}

multipaths {

multipath {

wwid 3600508b4000892b90002a00000050000 #磁盘的WWID

alias comsys-dm0 #映射后的别名，自己命名

path_grouping_policy multibus #路径组策略

path_checker tur #决定路径状态的方法

path_selector "round-robin 0" #选择那一条路径进行下次IO操作

}

multipath {

wwid 3600508b4000892b90002a00000090000

alias comsys-dm1

path_grouping_policy multibus

path_checker tur

path_selector "round-robin 0"

}

multipath {

wwid 3600508b4000892b90002a00000140000

alias comsys-backup

path_grouping_policy multibus

path_checker tur

path_selector "round-robin 0"

}

devices {

device {

vendor "HP" #厂商名称，可通过multipath –v3获取到

product "HSV300" #产品型号

path_grouping_policy multibus #默认的路径组策略

getuid_callout "/sbin/scsi_id -g -u -s /block/%n" #获得唯一设备号使用的默认程序

path_checker readsector0 #决定路径状态的方法

path_selector "round-robin 0" #选择那条路径进行下一个IO操作的方法

#failback immediate #故障恢复的模式

#no_path_retry queue #在disable queue之前系统尝试使用失效路径的次数的数值

#rr_min_io 100 #在当前的用户组中，在切换到另外一条路径之前的IO请求的数目

}

备注：

其中 wwid，vendor，product， getuid_callout这些参数可以通过：multipath -v3命令来获取。如果在/etc/multipath.conf中有设定各wwid别名,别名会覆盖此设定。

下面是两种方法来获取WWID
（1）默认情况下，将使用 /var/lib/multipath/bindings 内的配置设定具体每个多路径设备名，如果在/etc/multipath.conf中有设定各wwid 别名，别名会覆盖此设定。
[root@seaing ~]# cat /var/lib/multipath/bindings
# Multipath bindings, Version : 1.0
# NOTE: this file is automatically maintained by the multipath program.
# You should not need to edit this file in normal circumstances.
#
# Format:
# alias wwid
#
mpath0 SATA_WDC_WD5003ABYX-_WD-WMAYP4135415
mpath1 3600508b4000892b90002a00000050000
mpath2 3600508b4000892b90002a00000090000

（2）通过multipath -v3命令来获取

[root@seaing ~]# multipath -v3

dm-0: blacklisted

dm-1: blacklisted

dm-2: blacklisted

dm-3: blacklisted

dm-4: blacklisted

loop0: blacklisted

loop1: blacklisted

loop2: blacklisted

loop3: blacklisted

loop4: blacklisted

loop5: blacklisted

loop6: blacklisted

loop7: blacklisted

md0: blacklisted

ram0: blacklisted

ram10: blacklisted

ram11: blacklisted

ram12: blacklisted

ram13: blacklisted

ram14: blacklisted

ram15: blacklisted

ram1: blacklisted

ram2: blacklisted

ram3: blacklisted

ram4: blacklisted

ram5: blacklisted

ram6: blacklisted

ram7: blacklisted

ram8: blacklisted

ram9: blacklisted

sda: blacklisted

sdb: not found in pathvec

sdb: mask = 0x1f

sdb: bus = 1

sdb: dev_t = 8:16

sdb: size = 209715200

sdb: vendor = HP

sdb: product = HSV300

sdb: rev = 0952

sdb: h:b:t:l = 4:0:0:1

sdb: tgt_node_name = 0x50014380013be3f0

sdb: serial = P5512G29SVP02Q

sdb: path checker = readsector0 (controller setting)

sdb: checker timeout = 60000 ms (sysfs setting)

sdb: state = 2

sdb: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdb: uid = 3600508b4000892b90002a00000050000 (callout)

sdb: getprio = NULL (internal default)

sdb: prio = 1

sdc: not found in pathvec

sdc: mask = 0x1f

sdc: bus = 1

sdc: dev_t = 8:32

sdc: size = 419430400

sdc: vendor = HP

sdc: product = HSV300

sdc: rev = 0952

sdc: h:b:t:l = 4:0:0:2

sdc: tgt_node_name = 0x50014380013be3f0

sdc: serial = P5512G29SVP02Q

sdc: path checker = readsector0 (controller setting)

sdc: checker timeout = 60000 ms (sysfs setting)

sdc: state = 2

sdc: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdc: uid = 3600508b4000892b90002a00000090000 (callout)

sdc: getprio = NULL (internal default)

sdc: prio = 1

sdd: not found in pathvec

sdd: mask = 0x1f

sdd: bus = 1

sdd: dev_t = 8:48

sdd: size = 209715200

sdd: vendor = HP

sdd: product = HSV300

sdd: rev = 0952

sdd: h:b:t:l = 4:0:0:3

sdd: tgt_node_name = 0x50014380013be3f0

sdd: serial = P5512G29SVP02Q

sdd: path checker = readsector0 (controller setting)

sdd: checker timeout = 60000 ms (sysfs setting)

sdd: state = 2

sdd: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdd: uid = 3600508b4000892b90002a00000140000 (callout)

sdd: getprio = NULL (internal default)

sdd: prio = 1

sde: not found in pathvec

sde: mask = 0x1f

sde: bus = 1

sde: dev_t = 8:64

sde: size = 209715200

sde: vendor = HP

sde: product = HSV300

sde: rev = 0952

sde: h:b:t:l = 4:0:1:1

sde: tgt_node_name = 0x50014380013be3f0

sde: serial = P5512G29SVP01O

sde: path checker = readsector0 (controller setting)

sde: checker timeout = 60000 ms (sysfs setting)

sde: state = 2

sde: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sde: uid = 3600508b4000892b90002a00000050000 (callout)

sde: getprio = NULL (internal default)

sde: prio = 1

sdf: not found in pathvec

sdf: mask = 0x1f

sdf: bus = 1

sdf: dev_t = 8:80

sdf: size = 419430400

sdf: vendor = HP

sdf: product = HSV300

sdf: rev = 0952

sdf: h:b:t:l = 4:0:1:2

sdf: tgt_node_name = 0x50014380013be3f0

sdf: serial = P5512G29SVP01O

sdf: path checker = readsector0 (controller setting)

sdf: checker timeout = 60000 ms (sysfs setting)

sdf: state = 2

sdf: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdf: uid = 3600508b4000892b90002a00000090000 (callout)

sdf: getprio = NULL (internal default)

sdf: prio = 1

sdg: not found in pathvec

sdg: mask = 0x1f

sdg: bus = 1

sdg: dev_t = 8:96

sdg: size = 209715200

sdg: vendor = HP

sdg: product = HSV300

sdg: rev = 0952

sdg: h:b:t:l = 4:0:1:3

sdg: tgt_node_name = 0x50014380013be3f0

sdg: serial = P5512G29SVP01O

sdg: path checker = readsector0 (controller setting)

sdg: checker timeout = 60000 ms (sysfs setting)

sdg: state = 2

sdg: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdg: uid = 3600508b4000892b90002a00000140000 (callout)

sdg: getprio = NULL (internal default)

sdg: prio = 1

sdh: not found in pathvec

sdh: mask = 0x1f

sdh: bus = 1

sdh: dev_t = 8:112

sdh: size = 209715200

sdh: vendor = HP

sdh: product = HSV300

sdh: rev = 0952

sdh: h:b:t:l = 5:0:0:1

sdh: tgt_node_name = 0x50014380013be3f0

sdh: serial = P5512G29SVP02Q

sdh: path checker = readsector0 (controller setting)

sdh: checker timeout = 60000 ms (sysfs setting)

sdh: state = 2

sdh: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdh: uid = 3600508b4000892b90002a00000050000 (callout)

sdh: getprio = NULL (internal default)

sdh: prio = 1

sdi: not found in pathvec

sdi: mask = 0x1f

sdi: bus = 1

sdi: dev_t = 8:128

sdi: size = 419430400

sdi: vendor = HP

sdi: product = HSV300

sdi: rev = 0952

sdi: h:b:t:l = 5:0:0:2

sdi: tgt_node_name = 0x50014380013be3f0

sdi: serial = P5512G29SVP02Q

sdi: path checker = readsector0 (controller setting)

sdi: checker timeout = 60000 ms (sysfs setting)

sdi: state = 2

sdi: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdi: uid = 3600508b4000892b90002a00000090000 (callout)

sdi: getprio = NULL (internal default)

sdi: prio = 1

sdj: not found in pathvec

sdj: mask = 0x1f

sdj: bus = 1

sdj: dev_t = 8:144

sdj: size = 209715200

sdj: vendor = HP

sdj: product = HSV300

sdj: rev = 0952

sdj: h:b:t:l = 5:0:0:3

sdj: tgt_node_name = 0x50014380013be3f0

sdj: serial = P5512G29SVP02Q

sdj: path checker = readsector0 (controller setting)

sdj: checker timeout = 60000 ms (sysfs setting)

sdj: state = 2

sdj: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdj: uid = 3600508b4000892b90002a00000140000 (callout)

sdj: getprio = NULL (internal default)

sdj: prio = 1

sdk: not found in pathvec

sdk: mask = 0x1f

sdk: bus = 1

sdk: dev_t = 8:160

sdk: size = 209715200

sdk: vendor = HP

sdk: product = HSV300

sdk: rev = 0952

sdk: h:b:t:l = 5:0:1:1

sdk: tgt_node_name = 0x50014380013be3f0

sdk: serial = P5512G29SVP01O

sdk: path checker = readsector0 (controller setting)

sdk: checker timeout = 60000 ms (sysfs setting)

sdk: state = 2

sdk: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdk: uid = 3600508b4000892b90002a00000050000 (callout)

sdk: getprio = NULL (internal default)

sdk: prio = 1

sdl: not found in pathvec

sdl: mask = 0x1f

sdl: bus = 1

sdl: dev_t = 8:176

sdl: size = 419430400

sdl: vendor = HP

sdl: product = HSV300

sdl: rev = 0952

sdl: h:b:t:l = 5:0:1:2

sdl: tgt_node_name = 0x50014380013be3f0

sdl: serial = P5512G29SVP01O

sdl: path checker = readsector0 (controller setting)

sdl: checker timeout = 60000 ms (sysfs setting)

sdl: state = 2

sdl: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdl: uid = 3600508b4000892b90002a00000090000 (callout)

sdl: getprio = NULL (internal default)

sdl: prio = 1

sdm: not found in pathvec

sdm: mask = 0x1f

sdm: bus = 1

sdm: dev_t = 8:192

sdm: size = 209715200

sdm: vendor = HP

sdm: product = HSV300

sdm: rev = 0952

sdm: h:b:t:l = 5:0:1:3

sdm: tgt_node_name = 0x50014380013be3f0

sdm: serial = P5512G29SVP01O

sdm: path checker = readsector0 (controller setting)

sdm: checker timeout = 60000 ms (sysfs setting)

sdm: state = 2

sdm: getuid = /sbin/scsi_id -g -u -s /block/%n (controller setting)

sdm: uid = 3600508b4000892b90002a00000140000 (callout)

sdm: getprio = NULL (internal default)

sdm: prio = 1

sr0: blacklisted

===== paths list =====

uuid hcil dev dev_t pri dm_st chk_st vend/pr

3600508b4000892b90002a00000050000 4:0:0:1 sdb 8:16 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000090000 4:0:0:2 sdc 8:32 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000140000 4:0:0:3 sdd 8:48 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000050000 4:0:1:1 sde 8:64 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000090000 4:0:1:2 sdf 8:80 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000140000 4:0:1:3 sdg 8:96 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000050000 5:0:0:1 sdh 8:112 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000090000 5:0:0:2 sdi 8:128 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000140000 5:0:0:3 sdj 8:144 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000050000 5:0:1:1 sdk 8:160 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000090000 5:0:1:2 sdl 8:176 1 [undef][ready] HP,HSV3

3600508b4000892b90002a00000140000 5:0:1:3 sdm 8:192 1 [undef][ready] HP,HSV3

params = 0 0 1 1 round-robin 0 4 1 8:32 1000 8:80 1000 8:128 1000 8:176 1000

status = 2 0 0 0 1 1 A 0 4 0 8:32 A 0 8:80 A 0 8:128 A 0 8:176 A 0

params = 0 0 1 1 round-robin 0 4 1 8:16 1000 8:64 1000 8:112 1000 8:160 1000

status = 2 0 0 0 1 1 A 0 4 0 8:16 A 0 8:64 A 0 8:112 A 0 8:160 A 0

params = 0 0 1 1 round-robin 0 4 1 8:48 1000 8:96 1000 8:144 1000 8:192 1000

status = 2 0 0 0 1 1 A 0 4 0 8:48 A 0 8:96 A 0 8:144 A 0 8:192 A 0

sdb: ownership set to comsys-dm0

sdb: not found in pathvec

sdb: mask = 0xc

sdb: state = 2

sdb: prio = 1

sde: ownership set to comsys-dm0

sde: not found in pathvec

sde: mask = 0xc

sde: state = 2

sde: prio = 1

sdh: ownership set to comsys-dm0

sdh: not found in pathvec

sdh: mask = 0xc

sdh: state = 2

sdh: prio = 1

sdk: ownership set to comsys-dm0

sdk: not found in pathvec

sdk: mask = 0xc

sdk: state = 2

sdk: prio = 1

comsys-dm0: pgfailover = -1 (internal default)

comsys-dm0: pgpolicy = multibus (LUN setting)

comsys-dm0: selector = round-robin 0 (LUN setting)

comsys-dm0: features = 0 (internal default)

comsys-dm0: hwhandler = 0 (internal default)

comsys-dm0: rr_weight = 1 (internal default)

comsys-dm0: minio = 1000 (config file default)

comsys-dm0: no_path_retry = NONE (internal default)

pg_timeout = NONE (internal default)

comsys-dm0: set ACT_NOTHING (map unchanged)

sdc: ownership set to comsys-dm1

sdc: not found in pathvec

sdc: mask = 0xc

sdc: state = 2

sdc: prio = 1

sdf: ownership set to comsys-dm1

sdf: not found in pathvec

sdf: mask = 0xc

sdf: state = 2

sdf: prio = 1

sdi: ownership set to comsys-dm1

sdi: not found in pathvec

sdi: mask = 0xc

sdi: state = 2

sdi: prio = 1

sdl: ownership set to comsys-dm1

sdl: not found in pathvec

sdl: mask = 0xc

sdl: state = 2

sdl: prio = 1

comsys-dm1: pgfailover = -1 (internal default)

comsys-dm1: pgpolicy = multibus (LUN setting)

comsys-dm1: selector = round-robin 0 (LUN setting)

comsys-dm1: features = 0 (internal default)

comsys-dm1: hwhandler = 0 (internal default)

comsys-dm1: rr_weight = 1 (internal default)

comsys-dm1: minio = 1000 (config file default)

comsys-dm1: no_path_retry = NONE (internal default)

pg_timeout = NONE (internal default)

comsys-dm1: set ACT_NOTHING (map unchanged)

sdd: ownership set to comsys-backup

sdd: not found in pathvec

sdd: mask = 0xc

sdd: state = 2

sdd: prio = 1

sdg: ownership set to comsys-backup

sdg: not found in pathvec

sdg: mask = 0xc

sdg: state = 2

sdg: prio = 1

sdj: ownership set to comsys-backup

sdj: not found in pathvec

sdj: mask = 0xc

sdj: state = 2

sdj: prio = 1

sdm: ownership set to comsys-backup

sdm: not found in pathvec

sdm: mask = 0xc

sdm: state = 2

sdm: prio = 1

comsys-backup: pgfailover = -1 (internal default)

comsys-backup: pgpolicy = multibus (LUN setting)

comsys-backup: selector = round-robin 0 (LUN setting)

comsys-backup: features = 0 (internal default)

comsys-backup: hwhandler = 0 (internal default)

comsys-backup: rr_weight = 1 (internal default)

comsys-backup: minio = 1000 (config file default)

comsys-backup: no_path_retry = NONE (internal default)

pg_timeout = NONE (internal default)

comsys-backup: set ACT_NOTHING (map unchanged)

下面是相关参数的标准文档的介绍：

Attribute

Description

wwid

Specifies the WWID of the multipath device to which themultipath attributes apply. This parameter is mandatory for this section of themultipath.conf file.

alias

Specifies the symbolic name for the multipath device to which themultipath attributes apply. If you are usinguser_friendly_names, do not set this value tompathn; this may conflict with an automatically assigned user friendly name and give you incorrect device node names.

path_grouping_policy

Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include:

failover = 1 path per priority group

multibus = all valid paths in 1 priority group

group_by_serial = 1 priority group per detected serial number

group_by_prio = 1 priority group per path priority value

group_by_node_name = 1 priority group per target node name

path_selector

Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include:

round-robin 0: Loop through every path in the path group, sending the same amount of I/O to each.

queue-length 0: Send the next bunch of I/O down the path with the least number of outstanding I/O requests.

service-time 0: Send the next bunch of I/O down the path with the shortest estimated service time, which is determined by dividing the total size of the outstanding I/O to each path by its relative throughput.

failback

Manages path group failback.

A value of immediate specifies immediate failback to the highest priority path group that contains active paths.

A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention.

A value of followover specifies that automatic failback should be performed when the first path of a path group becomes active. This keeps a node from automatically failing back when another node requested the failover.

A numeric value greater than zero specifies deferred failback, expressed in seconds.

prio

Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitableprio value. Possible values include:

const: Set a priority of 1 to all paths.

emc: Generate the path priority for EMC arrays.

alua: Generate the path priority based on the SCSI-3 ALUA settings.

tpg_pref: Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit.

ontap: Generate the path priority for NetApp arrays.

rdac: Generate the path priority for LSI/Engenio RDAC controller.

hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode.

hds: Generate the path priority for Hitachi HDS Modular storage arrays.

no_path_retry

A numeric value for this attribute specifies the number of times the system should attempt to use a failed path before disabling queueing.

A value of fail indicates immediate failure, without queueing.

A value of queue indicates that queueing should not stop until the path is fixed.

rr_min_io

Specifies the number of I/O requests to route to a path before switching to the next path in the current path group. This setting is only for systems running kernels older that 2.6.31. Newer systems should userr_min_io_rq. The default value is 1000.

rr_min_io_rq

Specifies the number of I/O requests to route to a path before switching to the next path in the current path group, using request-based device-mapper-multipath. This setting should be used on systems running current kernels. On systems running kernels older than 2.6.31, use rr_min_io. The default value is 1.

rr_weight

If set to priorities, then instead of sending rr_min_iorequests to a path before calling path_selector to choose the next path, the number of requests to send is determined byrr_min_io times the path's priority, as determined by theprio function. If set to uniform, all path weights are equal.

flush_on_last_del

If set to yes, then multipath will disable queueing when the last path to a device has been deleted.

3、启动multipathd服务并设置其自动启动

[root@seaing ~]#service multipathd restart

[root@seaing ~]#chkconfig --level 345 multipathd on

[root@seaing ~]#chkconfig --list | grep multipathd

4、检查multipath聚合后的设备名，以及设备对应的链路情况

[root@seaing ~]# multipath -ll

comsys-dm1 (3600508b4000892b90002a00000090000) dm-3 HP,HSV300

[size=200G][features=0][hwhandler=0][rw]

\_ round-robin 0 [prio=4][active]

\_ 4:0:0:2 sdc 8:32 [active][ready]

\_ 4:0:1:2 sdf 8:80 [active][ready]

\_ 5:0:0:2 sdi 8:128 [active][ready]

\_ 5:0:1:2 sdl 8:176 [active][ready]

comsys-dm0 (3600508b4000892b90002a00000050000) dm-2 HP,HSV300

[size=100G][features=0][hwhandler=0][rw]

\_ round-robin 0 [prio=4][active]

\_ 4:0:0:1 sdb 8:16 [active][ready]

\_ 4:0:1:1 sde 8:64 [active][ready]

\_ 5:0:0:1 sdh 8:112 [active][ready]

\_ 5:0:1:1 sdk 8:160 [active][ready]

comsys-backup (3600508b4000892b90002a00000140000) dm-4 HP,HSV300

[size=100G][features=0][hwhandler=0][rw]

\_ round-robin 0 [prio=4][active]

\_ 4:0:0:3 sdd 8:48 [active][ready]

\_ 4:0:1:3 sdg 8:96 [active][ready]

\_ 5:0:0:3 sdj 8:144 [active][ready]

\_ 5:0:1:3 sdm 8:192 [active][ready]

5、检查配置是否成功

如果配置正确的话就会在/dev/mapper/目录下多出mpath0、mpath1（自动分配的名称）等之类设备，但是因为作者在配置的时候，起了别名，所以会使用别名来代替自动分配的名称

[root@seaing ~]# ll /dev/mapper/

total 0

brw-rw---- 1 root disk 253, 4 Oct 26 14:30 comsys-backup

brw-rw---- 1 root disk 253, 2 Oct 26 14:30 comsys-dm0

brw-rw---- 1 root disk 253, 3 Oct 26 14:30 comsys-dm1

crw------- 1 root root 10, 63 Oct 26 14:30 control

brw-rw---- 1 root disk 253, 0 Oct 26 14:30 VolGroup00-LogVol00

brw-rw---- 1 root disk 253, 1 Oct 26 14:30 VolGroup00-LogVol01

用fdisk -l命令可以看到多路径软件创建的磁盘，如下图中的/dev/dm-[0-3]

[root@seaing ~]# fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes

255 heads, 63 sectors/track, 60801 cylinders