RHEL5 多路径配置

1 检查软件包是否安装
[root@pcvmaster ~]# rpm -qa|grep device-mapper
device-mapper-libs-1.02.74-10.el6.x86_64
device-mapper-event-libs-1.02.74-10.el6.x86_64
device-mapper-multipath-0.4.9-56.el6.x86_64
device-mapper-1.02.74-10.el6.x86_64
device-mapper-event-1.02.74-10.el6.x86_64
device-mapper-multipath-libs-0.4.9-56.el6.x86_64
2 安装multipath
[root@pcvmaster ~]# yum -yinstall multipath
3 开机启动
[root@pcvmaster ~]# chkconfigmultipathd on
4 编辑multipath配置文件
vi /etc/multipath.conf
# This is a basicconfiguration file with some examples, for device mapper
# multipath.
# For a complete list of thedefault configuration values, see
#/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.defaults
# For a list of configurationoptions with descriptions, see
#/usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.annotated
#
# REMEMBER: After updatingmultipath.conf, you must run
#
# service multipathd reload
#
# for the changes to takeeffect in multipathd

## By default, devices withvendor = "IBM" and product = "S/390.*" are
## blacklisted. To enablemulitpathing on these devies, uncomment the
## following lines.
#blacklist_exceptions {
# device {
# vendor "IBM"
# product "S/390.*"
# }
#}

## Use user friendly names,instead of using WWIDs as names.
defaults {
user_friendly_names yes
}
##
## Here is an example of howto configure some standard options.
##
#
#defaults {
# udev_dir /dev
# polling_interval 10
# selector "round-robin0"
# path_grouping_policy multibus
# getuid_callout "/lib/udev/scsi_id--whitelisted --device=/dev/%n"
# prio alua
# path_checker readsector0
# rr_min_io 100
# max_fds 8192
# rr_weight priorities
# failback immediate
# no_path_retry fail
# user_friendly_names yes
#}
##
## The wwid line in thefollowing blacklist section is shown as an example
## of how to blacklistdevices by wwid. The 2 devnode lines arethe
## compiled in defaultblacklist. If you want to blacklist entire types
## of devices, such as allscsi devices, you should use a devnode line.
## However, if you want toblacklist specific devices, you should use
## a wwid line. Since there is no guarantee that a specificdevice will
## not change names on reboot（from /dev/sda to /dev/sdb for example）
## devnode lines are notrecommended for blacklisting specific devices.
##
#blacklist {
# wwid 26353900f02796769
# devnode "^（ram|raw|loop|fd|md|dm-|sr|scd|st）[0-9]*"
# devnode "^hd[a-z]"
#}
#multipaths {
# multipath {
# wwid 3600508b4000156d700012000000b0000
# alias yellow
# path_grouping_policy multibus
# path_checker readsector0
# path_selector "round-robin0"
# failback manual
# rr_weight priorities
# no_path_retry 5
# }
# multipath {
# wwid 1DEC_____321816758474
# alias red
# }
#}
#devices {
# device {
# vendor "COMPAQ "
# product "HSV110（C）COMPAQ"
# path_grouping_policy multibus
# getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
# path_checker readsector0
# path_selector "round-robin0"
# hardware_handler "0"
# failback 15
# rr_weight priorities
# no_path_retry queue
# }
# device {
# vendor "COMPAQ "
# product "MSA1000 "
# path_grouping_policy multibus
# }
#}

blacklist {
devnode"^（ram|raw|loop|fd|md|dm-|sr|sr|scd|st）[0-9]*"
devnode"^hd[a-z]"
}
devices {
device {
vendor"Netapp"
path_grouping_policymultibus
features "1queue_if_no_path"
path_checkerreadsector（）
failback immediate
}
}
5 启动服务
[root@pcvmaster ~]#/etc/init.d/multipathd start
6 删除现有没有使用的路径
[root@pcvmaster ~]# multipath–F
7 格式化路径，检测路径，合并路径
[root@pcvmaster ~]# multipath-v2
8 查看多路径状态
[root@pcvmaster ~]# multipath–ll
9 重启系统
[root@pcvmaster ~]# reboot
10创建PV多块磁盘,
[root@pcvmaster ~]# pvcreate/dev/mapper/mpath{d,f,e,p,t,k,j,c,s,q}
11添加多块磁盘到Volbackup
[root@pcvmaster~]# vgcreateVolbackup /dev/mapper/mpath{d,f,e,p,t,k,j,c,s,q}
12创建LV
[root@pcvmaster ~]# lvcreate-l 1310780 -n LogVol01 Volbackup
13格式化LV
[root@pcvmaster ~] mkfs.ext4/dev/Volbackup/LogVol01
14挂载
[root@pcvmaster ~]# mount/dev/Volbackup/LogVol01 /backup
15FAQ
15.1 模块没有加载成功后
如果模块没有加载成功请使用下列命初始化DM，或重启系统
---Use thefollowing commands to initialize and start DM for the first time:
# modprobedm-multipath
# modprobe dm-round-robin
# servicemultipathd start
# multipath –v2
15.2 multipath原理介绍
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devicemapper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。更多RedHat相关信息见RedHat 专题页面 http://www.linuxidc.com/topicnews.aspx？tid=10本文永久更新链接地址