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。

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

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/dm-2: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-2 doesn’t contain a valid partition table

Disk /dev/dm-3: 214.7 GB, 214748364800 bytes

255 heads, 63 sectors/track, 26108 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-3 doesn’t contain a valid partition table

Disk /dev/dm-4: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-4 doesn’t contain a valid partition table

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

total 0

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-backup -> ../dm-4

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm0 -> ../dm-2

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm1 -> ../dm-3

multipath基本操作命令
[root@seaing ~]#/etc/init.d/multipathd start #开启mulitipath服务
[root@seaing ~]#multipath -F    #删除现有路径
[root@seaing ~]#multipath -v2   #格式化路径
[root@seaing ~]#multipath -ll      #查看多路径

三、multipath的使用案例

要对多路径软件生成的磁盘进行操作直接操作/dev/mapper/目录下的磁盘就行。在对多路径软件生成的磁盘进行分区之前最好运行一下pvcreate命令:

[root@seaing ~]# pvcreate /dev/mapper/comsys-dm0

  Physical volume "/dev/mapper/comsys-dm0" successfully created

[root@seaing ~]#

[root@seaing ~]# pvs

  PV         VG         Fmt  Attr PSize   PFree

  /dev/dm-2             lvm2 --   100.00G 100.00G

  /dev/sda2  VolGroup00 lvm2 a-   465.66G      0

[root@seaing ~]# fdisk /dev/mapper/comsys-dm0

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel

Building a new DOS disklabel. Changes will remain in memory only,

until you decide to write them. After that, of course, the previous

content won't be recoverable.

The number of cylinders for this disk is set to 13054.

There is nothing wrong with that, but this is larger than 1024,

and could in certain setups cause problems with:

1) software that runs at boot time (e.g., old versions of LILO)

2) booting and partitioning software from other OSs

   (e.g., DOS FDISK, OS/2 FDISK)

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n

Command action

   e   extended

   p   primary partition (1-4)

Partition number (1-4): 1

First cylinder (1-13054, default 1):

Using default value 1

Last cylinder or +size or +sizeM or +sizeK (1-13054, default 13054): +10G

Command (m for help): p

Disk /dev/mapper/comsys-dm0: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

                  Device Boot      Start         End      Blocks   Id  System

/dev/mapper/comsys-dm0p1               1        1217     9775521   83  Linux

Command (m for help): n

Command action

   e   extended

   p   primary partition (1-4)

Partition number (1-4): 2

First cylinder (1218-13054, default 1218):

Using default value 1218

Last cylinder or +size or +sizeM or +sizeK (1218-13054, default 13054): +20G

Command (m for help): p

Disk /dev/mapper/comsys-dm0: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

                  Device Boot      Start         End      Blocks   Id  System

/dev/mapper/comsys-dm0p1               1        1217     9775521   83  Linux

/dev/mapper/comsys-dm0p2            1218        3650    19543072+  83  Linux

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 22: Invalid argument.

The kernel still uses the old table.

The new table will be used at the next reboot.

Syncing disks.

用fdisk对多路径软件生成的磁盘进行分区保存时会有一个报错,此报错不用理会。

[root@seaing ~]# fdisk -l

fdisk对多路径软件生成的磁盘进行分区之后，所生成的磁盘分区并没有马上添加到/dev/目录下，此时我们要重启IPSAN或者FCSAN的驱动，如果是用iscsi-initiator来连接IPSAN的重启ISCSI服务就可以发现所生成的磁盘分区了；如果是FCSAN的话，需要重新启动操作系统才能识别到。

[root@seaing ~]# ll /dev/dm*

brw-rw---- 1 root root 253, 2 Oct 26 14:20 /dev/dm-2

brw-rw---- 1 root root 253, 3 Oct 26 14:15 /dev/dm-3

brw-rw---- 1 root root 253, 4 Oct 26 14:15 /dev/dm-4

[root@seaing ~]#

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

total 0

brw-rw---- 1 root disk 253,  4 Oct 26 14:15 comsys-backup

brw-rw---- 1 root disk 253,  2 Oct 26 14:22 comsys-dm0

brw-rw---- 1 root disk 253,  3 Oct 26 14:15 comsys-dm1

crw------- 1 root root  10, 63 Oct 26 14:15 control

brw-rw---- 1 root disk 253,  0 Oct 26 14:15 VolGroup00-LogVol00

brw-rw---- 1 root disk 253,  1 Oct 26 14:15 VolGroup00-LogVol01

重启操作系统之后

如下的comsys-dm0p1和comsys-dm0p2就是我们对multipath磁盘进行的分区

[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,  5 Oct 26 14:35 comsys-dm0p1

brw-rw---- 1 root disk 253,  6 Oct 26 14:30 comsys-dm0p2

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

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

[root@seaing ~]# ll /dev/dm*

brw-rw---- 1 root root 253, 2 Oct 26 14:30 /dev/dm-2

brw-rw---- 1 root root 253, 3 Oct 26 14:30 /dev/dm-3

brw-rw---- 1 root root 253, 4 Oct 26 14:30 /dev/dm-4

brw-rw---- 1 root root 253, 5 Oct 26 14:30 /dev/dm-5

brw-rw---- 1 root root 253, 6 Oct 26 14:30 /dev/dm-6

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

total 0

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-backup -> ../dm-4

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm0 -> ../dm-2

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm0p1 -> ../dm-5

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm0p2 -> ../dm-6

lrwxrwxrwx 1 root root 7 Oct 26 14:30 comsys-dm1 -> ../dm-3

[root@seaing ~]# fdisk -l

Disk /dev/dm-5: 10.0 GB, 10010133504 bytes

255 heads, 63 sectors/track, 1216 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-5 doesn't contain a valid partition table

Disk /dev/dm-6: 20.0 GB, 20012106240 bytes

255 heads, 63 sectors/track, 2433 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-6 doesn't contain a valid partition table

对comsys-dm0p1分区格式化成ext3文件系统

[root@seaing ~]# mkfs.ext3 /dev/mapper/comsys-dm0p1

mke2fs 1.39 (29-May-2006)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

1224000 inodes, 2443880 blocks

122194 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=2503999488

75 block groups

32768 blocks per group, 32768 fragments per group

16320 inodes per group

Superblock backups stored on blocks:

        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Writing inode tables: done

Creating journal (32768 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 27 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/VolGroup00-LogVol00

                      434G  8.4G  404G   3% /

/dev/sda1              99M   18M   77M  19% /boot

tmpfs                 7.9G     0  7.9G   0% /dev/shm

/software/rhel5.5-x86_64.iso

                      3.5G  3.5G     0 100% /mnt/dvd

将/dev/mapper/comsys-dm0p1挂载到/comsys目录下

 [root@seaing ~]# mount /dev/mapper/comsys-dm0p1 /comsys/

[root@seaing ~]#

[root@seaing ~]# df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/VolGroup00-LogVol00

                      434G  8.4G  404G   3% /

/dev/sda1              99M   18M   77M  19% /boot

tmpfs                 7.9G     0  7.9G   0% /dev/shm

/software/rhel5.5-x86_64.iso

                      3.5G  3.5G     0 100% /mnt/dvd

/dev/mapper/comsys-dm0p1

                      9.2G  150M  8.6G   2% /comsys

当然，也可以将磁盘创建成物理卷，然后在物理卷基础上创建卷组，然后创建逻辑卷，最后在格式化成文件系统进行挂载，下面的案例就是通过这种方法实现的（注意：下面的案例与上面的案例并没有联系，读者朋友请注意！）

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

total 0

brw-rw---- 1 root disk 253,  4 Oct 25 11:14 comsys-backup

brw-rw---- 1 root disk 253,  2 Oct 25 11:14 comsys-dm0

brw-rw---- 1 root disk 253,  5 Oct 25 11:14 comsys-dm0p1

brw-rw---- 1 root disk 253,  6 Oct 25 11:14 comsys-dm0p2

brw-rw---- 1 root disk 253,  7 Oct 25 11:14 comsys-dm0p3

brw-rw---- 1 root disk 253,  3 Oct 25 11:14 comsys-dm1

crw------- 1 root root  10, 63 Oct 25 11:14 control

brw-rw---- 1 root disk 253,  0 Oct 25 11:14 VolGroup00-LogVol00

brw-rw---- 1 root disk 253,  1 Oct 25 11:14 VolGroup00-LogVol01

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# mkdir /backup

[root@seaing ~]#

[root@seaing ~]# mount /dev/mapper/comsys-backup /backup

mount: you must specify the filesystem type

[root@seaing ~]# pvs

  PV         VG         Fmt  Attr PSize   PFree

  /dev/sda2  VolGroup00 lvm2 a-   465.66G    0

[root@seaing ~]#

[root@seaing ~]# vgs

  VG         #PV #LV #SN Attr   VSize   VFree

  VolGroup00   1   2   0 wz--n- 465.66G    0

[root@seaing ~]#

[root@seaing ~]# lvs

  LV       VG         Attr   LSize   Origin Snap%  Move Log Copy%  Convert

  LogVol00 VolGroup00 -wi-ao 448.03G

  LogVol01 VolGroup00 -wi-ao  17.62G

[root@seaing ~]#

[root@seaing ~]# pvcreate /dev/mapper/comsys-backup

  Physical volume "/dev/mapper/comsys-backup" successfully created

[root@seaing ~]#

[root@seaing ~]# pvs

  PV         VG         Fmt  Attr PSize   PFree

  /dev/dm-4             lvm2 --   100.00G 100.00G

  /dev/sda2  VolGroup00 lvm2 a-   465.66G      0

[root@seaing ~]#

[root@seaing ~]# vgcreate vg_backup /dev/mapper/comsys-backup

  Volume group "vg_backup" successfully created

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# vgs

  VG         #PV #LV #SN Attr   VSize   VFree

  VolGroup00   1   2   0 wz--n- 465.66G      0

  vg_backup    1   0   0 wz--n- 100.00G 100.00G

[root@seaing ~]#

[root@seaing ~]# pvs

  PV         VG         Fmt  Attr PSize   PFree

  /dev/dm-4  vg_backup  lvm2 a-   100.00G 100.00G

  /dev/sda2  VolGroup00 lvm2 a-   465.66G      0

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# lvcreate -L 20G -n lv_backup vg_backup

  Logical volume "lv_backup" created

[root@seaing ~]#

[root@seaing ~]# lvs

  LV        VG         Attr   LSize   Origin Snap%  Move Log Copy%  Convert

  LogVol00  VolGroup00 -wi-ao 448.03G

  LogVol01  VolGroup00 -wi-ao  17.62G

  lv_backup vg_backup  -wi-a-  20.00G

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# mkfs.ext3 /dev/vg_backup/lv_backup

mke2fs 1.39 (29-May-2006)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

2621440 inodes, 5242880 blocks

262144 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=4294967296

160 block groups

32768 blocks per group, 32768 fragments per group

16384 inodes per group

Superblock backups stored on blocks:

        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,

Writing inode tables: done

Creating journal (32768 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 20 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@seaing ~]#

[root@seaing ~]#

[root@seaing ~]# mount /dev/vg_backup/lv_backup /backup

[root@seaing ~]# df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/VolGroup00-LogVol00

                      434G  4.9G  407G   2% /

/dev/sda1              99M   18M   77M  19% /boot

tmpfs                 7.9G     0  7.9G   0% /dev/shm

/dev/mapper/vg_backup-lv_backup

                       20G  173M   19G   1% /backup

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