Linux自带多路径详解

Linux自带多路径详解

   一、多路径解释
  多路径,顾名思义就是有多种选择的路径。在SAN或IPSAN环境,主机和存储之间外加了光纤交换机,这就导致主机和存储之间交换速度和效率增强,一条路径肯定是不行的,也是不安全不稳定的。多路径就是要来解决从主机到磁盘之间最快,最高效的问题。主要实现如下几个功能
  故障的切换和恢复
  IO流量的负载均衡
  磁盘的虚拟化
  多路径之前一直是存储厂商负责解决,竟来被拆分出来单独卖钱了。
  构架基本是这样的:存储,多路径软件,光纤交换机,主机,主机系统。
   二、LINUX下的multipath
  1、查看是否自带安装?
  [root@web2 multipath]# rpm -qa|grep device
  device-mapper-1.02.39-1.el5
  device-mapper-1.02.39-1.el5
  device-mapper-multipath-0.4.7-34.el5
  device-mapper-event-1.02.39-1.el5
  [root@web2 multipath]#
  2、安装
  rpm -ivh device-mapper-1.02.39-1.el5.rpm    #安装映射包
  rpm -ivh device-mapper-multipath-0.4.7-34.el5.rpm  #安装多路径包
  外加加入开机启动
  chkconfig –level 2345 multipathd on          #设置成开机自启动multipathd
  lsmod |grep dm_multipath                      #来检查安装是否正常
  3、配置
# on the default devices.
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|sr|scd|st)[0-9]*"
devnode "^hd[a-z]"
}
devices {
device {
vendor "HP"
path_grouping_policy multibus
features "1 queue_if_no_path"
path_checker readsector()
failback immediate
}
}<br><br>完整的配置如下:
blacklist {
devnode "^sda"
}
defaults {
user_friendly_names no
}
multipaths {
multipath {
wwid                    14945540000000000a67854c6270b4359c66c272e2f356321
alias                   iscsi-dm0
path_grouping_policy    multibus
path_checker            tur
path_selector           "round-robin 0"
}
multipath {
wwid                    14945540000000000dcca2eda91d70b81edbcfce2357f99ee
alias                   iscsi-dm1
path_grouping_policy    multibus
path_checker            tur
path_selector           "round-robin 0"
}
multipath {
wwid                    1494554000000000020f763489c165561101813333957ed96
alias                   iscsi-dm2
path_grouping_policy    multibus
path_checker            tur
path_selector           "round-robin 0"
}
multipath {
wwid                    14945540000000000919ca813020a195422ba3663e1f03cc3
alias                   iscsi-dm3
path_grouping_policy    multibus
path_checker            tur
path_selector           "round-robin 0"
}
}
devices {
device {
vendor                  "iSCSI-Enterprise"
product                 "Virtual disk"
path_grouping_policy    multibus
getuid_callout          "/sbin/scsi_id -g -u -s /block/%n"
path_checker            readsector0
path_selector           "round-robin 0"
}
}
  4、命令
[root@web2 ~]# multipath -h
multipath-tools v0.4.7 (03/12, 2006)
Usage: multipath        [-v level] [-d] [-h|-l|-ll|-f|-F|-r]
[-p failover|multibus|group_by_serial|group_by_prio]
[device]
-v level        verbosity level
0                    no output
1                    print created devmap names only
2                    default verbosity
3                    print debug information
-h              print this usage text
-b file         bindings file location
-d              dry run, do not create or update devmaps
-l              show multipath topology (sysfs and DM info)
-ll             show multipath topology (maximum info)
-f              flush a multipath device map
-F              flush all multipath device maps
-r              force devmap reload
-p policy       force all maps to specified policy :
failover             1 path per priority group
multibus             all paths in 1 priority group
group_by_serial      1 priority group per serial
group_by_prio        1 priority group per priority lvl
group_by_node_name   1 priority group per target node
device          limit scope to the device's multipath
(udev-style $DEVNAME reference, eg /dev/sdb
or major:minor or a device map name)
[root@web2 ~]#
   5、启动关闭
  # /etc/init.d/multipathd start      #开启mulitipath服务
  service multipath start
  service multipath restart
  service multipath shutdown
   6、如何获取wwid
  1、
  [root@vxfs01 ~]# 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 36006016051d50e0035744871c912de11
  mpath1 36006016051d50e0034744871c912de11
  mpath2 36006016051d50e0032744871c912de11
  mpath3 36006016051d50e0039744871c912de11
  mpath4 36006016051d50e003a744871c912de11
  2、
  [root@vxfs01 ~]# multipath -v3 |grep 3600
  sdb: uid = 36006016051d50e003a744871c912de11 (callout)
  sdc: uid = 36006016051d50e003a744871c912de11 (callout)
  sdd: uid = 36006016051d50e003a744871c912de11 (callout)
  sde: uid = 36006016051d50e003a744871c912de11 (callout)
  36006016051d50e003a744871c912de11 1:0:0:0 sdb 8:16  0   [undef][ready] DGC,RAI
  36006016051d50e003a744871c912de11 1:0:1:0 sdc 8:32  1   [undef][ready] DGC,RAI
  36006016051d50e003a744871c912de11 2:0:0:0 sdd 8:48  1   [undef][ready] DGC,RAI
  36006016051d50e003a744871c912de11 2:0:1:0 sde 8:64  0   [undef][ready] DGC,RAI
  Found matching wwid [36006016051d50e003a744871c912de11] in bindings file.

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