相信做过Mutipath Device的童鞋对multipath.conf并不陌生。不错，这个是DM的配置文件。初次配置DM可以不修改配置文件中的任何内容，它会默认加载，当然用的参数也是默认的。有些时候我们的存储并不支持默认的配置，或者默认的配置并不适合存储的需求，这就需要对默认的参数做些修改。

 

    下面看一下默认mutipath.conf的内容：

[root@ProsDB01 etc]# more multipath.conf

# This is a basic configuration file with some examples, for device mapper # multipath. # For a complete list of the default configuration values, see # /usr/share/doc/device-mapper-multipath-0.4.7/multipath.conf.defaults # For a list of configuration options with descriptions, see # /usr/share/doc/device-mapper-multipath-0.4.7/multipath.conf.annotated

# Blacklist all devices by default. Remove this to enable multipathing

# on the default devices.

blacklist {

        devnode "*"

}

## By default, devices with vendor = "IBM" and product = "S/390.*" are

## blacklisted. To enable mulitpathing 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 how to configure some standard options. ## # #defaults { #       udev_dir                /dev #       polling_interval        10 #       selector                "round-robin 0" #       path_grouping_policy    multibus #       getuid_callout          "/sbin/scsi_id -g -u -s /block/%n" #       prio_callout            /bin/true #       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 the following blacklist section is shown as an example ## of how to blacklist devices by wwid.  The 2 devnode lines are the ## compiled in default blacklist. If you want to blacklist entire types ## of devices, such as all scsi devices, you should use a devnode line. ## However, if you want to blacklist specific devices, you should use ## a wwid line.  Since there is no guarantee that a specific device will ## not change names on reboot (from /dev/sda to /dev/sdb for example) ## devnode lines are not recommended 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-robin 0" #               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          "/sbin/scsi_id -g -u -s /block/%n" #               path_checker            readsector0 #               path_selector           "round-robin 0" #               hardware_handler        "0" #               failback                15 #               rr_weight               priorities #               no_path_retry           queue #       } #       device { #               vendor                  "COMPAQ  " #               product                 "MSA1000         " #               path_grouping_policy    multibus #       } #}

其中包含了几项参数：blacklist、defaults、multipaths、devices。这些参数对多路径的初始化信息起着决定性的作用。

    这里简单介绍下这个参数的作用，详细内容可参见官方文档：。

 

1、blacklist

这个参数用作排除磁盘的。有些磁盘比如本地盘已经做了Raid，这里就需要将本地盘和光驱设备排除，不配置多路径。语法格式配置文件中也有，一般情况sda是作为本地磁盘：

blacklist {

        devnode "^sda" }

当然，官方的建议还是采用WWID排除的方式，因为有些时候本地盘不只一个，名字也容易发生变化。

blacklist {

      wwid 26353900f02796769 #       devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*" #       devnode "^hd[a-z]" }

WWID号可以通过multipath -ll查看，或者

/sbin/scsi_id -g -s /block/sdb

 

2、defaults

这个参数是个全局参数，如果设置了，针对所有的盘是生效的。

 

3、multipaths

这个参数是针对一个盘的，配置一个盘得相关属性

 

4、devices

这个参数是针对设备的，不同存储对应不同的vendor。有些时候存储上的盘并不能被DM识别到，需要在devices参数中加入存储相关的参数。优先级要高于multipaths，比如path_grouping_policy在multipath设置为multibus，而在devices中设置为failover，那么生效的是failover。

 

这些了解了再看一下具体的参数，虽然很多，需要改动的很少。下面是比较重要的2个参数：

path_grouping_policy  

这个参数常用的两个：multipath failover，前者做负载均衡，后者是主备方式

 

path_checker 

这个参数要根据存储类型来定。常见的几种：readsector0, tur, emc_clariion, hp_sw,  directio。