LVM原理及详细操作

LVM

LVM是在磁盘分区和文件系统之间添加的一个逻辑层，来为文件系统屏蔽下层磁盘分区布局，提供一个抽象的盘卷，在盘卷上建立文件系统。首

先我们讨论以下几个LVM术语：

*物理存储介质（The physical media）

这里指系统的存储设备：硬盘，是存储系统最低层的存储单元。

*物理卷（physical volume）

物理卷就是指硬盘分区或从逻辑上与磁盘分区具有同样功能的设备

（如RAID），是LVM的基本存储逻辑块，但和基本的物理存储介质（如分区、磁盘等）比较，却包含有与LVM相关的管理参数。

*卷组（Volume Group）

LVM卷组类似于非LVM系统中的物理硬盘，其由物理卷组成。可以在卷组上创建一个或多个“LVM分区”（逻辑卷），LVM卷组由一个或多个物理卷组成。

*逻辑卷（logical volume）

LVM的逻辑卷类似于非LVM系统中的硬盘分区，在逻辑卷之上可以建立文件系统（比如/home或者/usr等）。

*PE（physical extent）

每一个物理卷被划分为称为PE(PhysicalExtents）的基本单元，具有

唯一编号的PE是可以被LVM寻址的最小单元。PE的大小是可配置的，默认为4MB。

*LE（logical extent）

逻辑卷也被划分为被称为LE(LogicalExtents）的可被寻址的基本单位。在同一个卷组中，LE的大小和PE是相同的，并且一一对应。

首先可以看到，物理卷（PV）被由大小等同的基本单元PE组成。

一个卷组由一个或多个物理卷组成。

从上图可以看到，PE和LE有着一一对应的关系。逻辑卷建立在卷组上。逻辑卷就相当于非LVM系统的磁盘分区，可以在其上创建文件系统。

下图是磁盘分区、卷组、逻辑卷和文件系统之间的逻辑关系的示意图：和非LVM系统将包含分区信息的元数据保存在位于分区的起始位置的

分区表中一样，逻辑卷以及卷组相关的元数据也是保存在位于物理卷起始

处的VGDA（卷组描述符区域）中。VGDA包括以下内容：PV描述符、VG描

述符、LV描述符、和一些PE描述符。

系统启动LVM时激活VG，并将VGDA加载至内存，来识别LV的实际物理存储位置。当系统进行I/O操作时，就会根据VGDA建立的映射机制来访

问实际的物理位置。

LVM操作：

//查看物理磁盘状态

(none):/home/liuzq/Desktop # fdisk -l

Disk /dev/sda: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk identifier: 0x000cd6a5

Device Boot Start End Blocks Id System

/dev/sda1 1 143 1148616 82 Linux swap / Solaris

/dev/sda2 * 144 13054 103707607+ 83 Linux

Disk /dev/sdb: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table

//使用fdisk对/dev/sdb分区

(none):/home/liuzq/Desktop # fdisk /dev/sdb

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

Building a new DOS disklabel with disk identifier 0xe5260b42.

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)

//创建新分区

Command (m for help): new

Command action

e extended

p primary partition (1-4)

//设置成主分区

p

Partition number (1-4): 1

First cylinder (1-13054, default 1):

Using default value 1

Last cylinder, +cylinders or +size{K,M,G} (1-13054, default 13054):

Using default value 13054

Command (m for help): m

Command action

a toggle a bootable flag

b edit bsd disklabel

c toggle the dos compatibility flag

d delet

e a partition

l list known partition types

m print this menu

n add a new partition

o create a new empty DOS partition table

p print the partition table

q quit without saving changes

s create a new empty Sun disklabel

t change a partition's system id

u change display/entry units

v verify the partition table

w write table to disk and exit

x extra functionality (experts only)

//继续下一步操作之前 先确认对相应分区的修改正确无误。如果一切妥当 则写入新分区表

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

//查看分区后的物理磁盘

(none):/home/liuzq/Desktop # fdisk -l

Disk /dev/sda: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk identifier: 0x000cd6a5

Device Boot Start End Blocks Id System

/dev/sda1 1 143 1148616 82 Linux swap / Solaris

/dev/sda2 * 144 13054 103707607+ 83 Linux

Disk /dev/sdb: 107.3 GB, 107374182400 bytes

255 heads, 63 sectors/track, 13054 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Disk identifier: 0xe5260b42

Device Boot Start End Blocks Id System

/dev/sdb1 1 13054 104856223+ 83 Linux

//进入LVM模式

(none):/home/liuzq/Desktop # lvm

//查看LVM磁盘状态----目前没有任何LVM磁盘信息

lvm> lvmdiskscan

/dev/sda1 [ 1.10 GB]

/dev/root [ 98.90 GB]

/dev/sdb1 [ 100.00 GB]

1 disk

2 partitions

0 LVM physical volume whole disks

0 LVM physical volumes

//查看LVM的配置文件

lvm> dumpconfig

devices {

dir="/dev"

scan="/dev"

filter=["r|/dev/.*/by-path/.*|", "r|/dev/.*/by-id/.*|", "a/.*/"]

cache="/etc/lvm/.cache"

write_cache_state=1

sysfs_scan=1

md_component_detection=1

}

dmeventd {

mirror_library="libdevmapper-event-lvm2mirror.so.2.02"

snapshot_library="libdevmapper-event-lvm2snapshot.so.2.02"

}

activation {

missing_stripe_filler="/dev/ioerror"

mirror_region_size=512

reserved_stack=256

reserved_memory=8192

process_priority=-18

}

global {

umask=63

test=0

activation=1

proc="/proc"

locking_type=1

locking_dir="/var/lock/lvm"

}

shell {

history_size=100

}

backup {

backup=1

backup_dir="/etc/lvm/backup"

archive=1

archive_dir="/etc/lvm/archive"

retain_min=10

retain_days=30

}

log {

verbose=0

syslog=1

overwrite=0

level=0

indent=1

command_names=0

prefix=" "

}

//创建PV

lvm> pvcreate /dev/sdb1

No physical volume label read from /dev/sdb1

Physical volume "/dev/sdb1" successfully created

//查看PV状态

lvm> pvdisplay

"/dev/sdb1" is a new physical volume of "100.00 GB"

--- NEW Physical volume ---

PV Name /dev/sdb1

VG Name

PV Size 100.00 GB

Allocatable NO

PE Size (KByte) 0

Total PE 0

Free PE 0

Allocated PE 0

PV UUID 7daSq9-7KXU-Lvil-SUHc-ELrI-fyX7-FM9Bfy

//再次查看LVM磁盘状态

lvm> lvmdiskscan

/dev/sda1 [ 1.10 GB]

/dev/root [ 98.90 GB]

/dev/sdb1 [ 100.00 GB] LVM physical volume

1 disk

1 partition

0 LVM physical volume whole disks

1 LVM physical volume

//创建VG

lvm> vgcreate vg_test /dev/sdb1

Volume group "vg_test" successfully created

//查看VG状态

lvm> vgdisplay

--- Volume group ---

VG Name vg_test

System ID

Format lvm2

Metadata Areas 1

Metadata Sequence No 1

VG Access read/write

VG Status resizable

MAX LV 0

Cur LV 0

Open LV 0

Max PV 0

Cur PV 1

Act PV 1

VG Size 100.00 GB

PE Size 4.00 MB

Total PE 25599

Alloc PE / Size 0 / 0

Free PE / Size 25599 / 100.00 GB

VG UUID oSUogC-mV2F-b7Dg-5sFa-tztZ-NDh4-fpL6zu

//查看所有VG

lvm> vgs

VG #PV #LV #SN Attr VSize VFree

vg_test 1 0 0 wz--n- 100.00G 100.00G

//创建LV

lvm> lvcreate --size 10G --name lvm_u1 vg_test

Logical volume "lvm_u1" created

//查看LV状态

lvm> lvs

LV VG Attr LSize Origin Snap% Move Log Copy%

Convert

lvm_u1 vg_test -wi-a- 10.00G

lvm> vgs

VG #PV #LV #SN Attr VSize VFree

vg_test 1 1 0 wz--n- 100.00G 90.00G

//退出LVM配置模式

lvm> exit

Exiting.

//ext3格式化逻辑卷

(none):/home/liuzq/Desktop # mkfs -t ext3 -j /dev/vg_test/lvm_u1

mke2fs 1.41.1 (01-Sep-2008)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

655360 inodes, 2621440 blocks

131072 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=2684354560

80 block groups

32768 blocks per group, 32768 fragments per group

8192 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 26 mounts or

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

//使用LVM

// 首先创建挂载点

(none):/home/liuzq/Desktop # mkdir /mnt/u1

//挂载卷

(none):/home/liuzq/Desktop # mount /dev/vg_test/lvm_u1 /mnt/u1/

//检查磁盘空间

(none):/home/liuzq/Desktop # df -m /mnt/u1/

Filesystem 1M-blocks Used Available Use% Mounted on

/dev/mapper/vg_test-lvm_u1

10080 151 9417 2% /mnt/u1

(none):/home/liuzq/Desktop # ls /mnt/u1/

lost+found

(none):/home/liuzq/Desktop # ll /boot/

total 14056

-rw------- 1 root root 512 2012-12-20 09:15 backup_mbr lrwxrwxrwx 1 root root 1 2012-12-20 09:00 boot -> .

-rw-r--r-- 1 root root 1236 2009-02-24 06:40 boot.readme -rw-r--r-- 1 root root 90137 2009-02-28 03:09 config-2.6.27.19-5-default

drwxr-xr-x 2 root root 568 2012-12-20 09:15 grub

lrwxrwxrwx 1 root root 26 2012-12-20 09:21 initrd -> initrd-2.6.27.19-5-default

-rw-r--r-- 1 root root 6199394 2012-12-20 09:21 initrd-2.6.27.19-5-default

-rw-r--r-- 1 root root 435200 2012-12-20 09:15 message

-rw-r--r-- 1 root root 141206 2009-02-28 03:13 symsets-2.6.27.19-5-default.tar.gz

-rw-r--r-- 1 root root 404804 2009-02-28 03:12 symtypes-2.6.27.19-5-default.gz

-rw-r--r-- 1 root root 119580 2009-02-28 03:10 symvers-2.6.27.19-5-default.gz

-rw-r--r-- 1 root root 1419451 2009-02-28 03:01 System.map-2.6.27.19-5-default

-rw-r--r-- 1 root root 3004323 2009-02-28 03:09 vmlinux-2.6.27.19-5-default.gz

lrwxrwxrwx 1 root root 27 2012-12-20 09:06 vmlinuz -> vmlinuz-2.6.27.19-5-default

-rw-r--r-- 1 root root 2537184 2009-02-28 03:01 vmlinuz-2.6.27.19-5-default

//在新建文件系统里复制一个大文件 例如 在/boot目录里挑个内核文件 复制到/mnt/u1

(none):/home/liuzq/Desktop # cp /boot/vmlinux-2.6.27.19-5-default.gz /mnt/u1/

//对复制过来的文件运行md5sum 并保存校验值 留待后用

(none):/home/liuzq/Desktop # md5sum /mnt/u1/vmlinux-2.6.27.19-5-default.gz

71603654a26edc4faa85054cbe2900be

/mnt/u1/vmlinux-2.6.27.19-5-default.gz

(none):/home/liuzq/Desktop # ll /mnt/u1/

total 2956

drwx------ 2 root root 16384 2013-01-05 01:43 lost+found

-rw-r--r-- 1 root root 3004323 2013-01-05 01:51

vmlinux-2.6.27.19-5-default.gz

//扩大LVM卷

假定空间不够用 准备向LVM卷增加更多空间。首先 卸载该卷 并使用lvresize命令调整卷大小。然后 还必须用e2fsck检查整个文件系统 并运行resize2fs调整该卷上ext3文件系统的大小

//卸载

(none):/home/liuzq/Desktop # umount /mnt/u1/

//调整卷大小

(none):/home/liuzq/Desktop # lvresize --size 20G /dev/vg_test/lvm_u1

Extending logical volume lvm_u1 to 20.00 GB

Logical volume lvm_u1 successfully resized

//检查文件系统

(none):/home/liuzq/Desktop # e2fsck -f /dev/vg_test/lvm_u1 e2fsck 1.41.1 (01-Sep-2008)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/vg_test/lvm_u1: 12/655360 files (0.0% non-contiguous), 80431/2621440 blocks

//调整文件系统大小

(none):/home/liuzq/Desktop # resize2fs /dev/vg_test/lvm_u1 20G resize2fs 1.41.1 (01-Sep-2008)

Resizing the filesystem on /dev/vg_test/lvm_u1 to 5242880 (4k) blocks.

The filesystem on /dev/vg_test/lvm_u1 is now 5242880 blocks long.

在上面的例子中 卷和文件系统的大小都调整为20G。下面重新挂载卷 检查磁盘空间和之前计算的md5sum

//重新挂载

(none):/home/liuzq/Desktop # mount /dev/vg_test/lvm_u1 /mnt/u1

(none):/home/liuzq/Desktop # df -m /mnt/u1/

Filesystem 1M-blocks Used Available Use%

Mounted on

/dev/mapper/vg_test-lvm_u1

20159 159 18977 1%

/mnt/u1

(none):/home/liuzq/Desktop # ll /mnt/u1/

total 2956

drwx------ 2 root root 16384 2013-01-05 01:43 lost+found

-rw-r--r-- 1 root root 3004323 2013-01-05 01:51

vmlinux-2.6.27.19-5-default.gz

(none):/home/liuzq/Desktop # md5sum

/mnt/u1/vmlinux-2.6.27.19-5-default.gz

71603654a26edc4faa85054cbe2900be

/mnt/u1/vmlinux-2.6.27.19-5-default.gz

(none):/home/liuzq/Desktop # lvm

lvm> lvs

LV VG Attr LSize Origin Snap% Move Log Copy%

Convert

lvm_u1 vg_test -wi-ao 20.00G

lvm> vgs

VG #PV #LV #SN Attr VSize VFree

vg_test 1 1 0 wz--n- 100.00G 80.00G

lvm> lvdisplay

--- Logical volume ---

LV Name /dev/vg_test/lvm_u1

VG Name vg_test

LV UUID hO9SlO-6t9u-nHfE-tm0V-SQPC-827D-1EksZT

LV Write Access read/write

LV Status available

# open 1

LV Size 20.00 GB

Current LE 5120

Segments 1

Allocation inherit

Read ahead sectors auto

- currently set to 256

Block device 253:0

lvm> exit

Exiting.

(none):/home/liuzq/Desktop #

(none):/home/liuzq/Desktop # lvs

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

lvm_u1 vg_test -wi-ao 20.00G

缩小LVM卷

缩减现有LVM卷里不需要的空间时也可以使用lvresize。和前面一样 在调整卷大小之前先卸载这个卷 然后运行e2fsck 检查文件系统 和resize2fs 调整成较小尺寸

(none):/home/liuzq/Desktop # umount /mnt/u1/

(none):/home/liuzq/Desktop # e2fsck -f /dev/vg_test/lvm_u1 e2fsck 1.41.1 (01-Sep-2008)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/vg_test/lvm_u1: 12/1310720 files (0.0% non-contiguous), 122833/5242880 blocks

(none):/home/liuzq/Desktop # resize2fs /dev/vg_test/lvm_u1 15G resize2fs 1.41.1 (01-Sep-2008)

Resizing the filesystem on /dev/vg_test/lvm_u1 to 3932160 (4k) blocks.

The filesystem on /dev/vg_test/lvm_u1 is now 3932160 blocks long.

(none):/home/liuzq/Desktop # lvresize --size 15G /dev/vg_test/lvm_u1

WARNING: Reducing active logical volume to 15.00 GB

THIS MAY DESTROY YOUR DATA (filesystem etc.)

Do you really want to reduce lvm_u1? [y/n]: y

Reducing logical volume lvm_u1 to 15.00 GB

Logical volume lvm_u1 successfully resized

(none):/home/liuzq/Desktop # mount /dev/vg_test/lvm_u1 /mnt/u1/

(none):/home/liuzq/Desktop # lvs

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

lvm_u1 vg_test -wi-ao 15.00G (none):/home/liuzq/Desktop # vgs

VG #PV #LV #SN Attr VSize VFree

vg_test 1 1 0 wz--n- 100.00G 85.00G

(none):/home/liuzq/Desktop # ll /mnt/u1/

total 2956

drwx------ 2 root root 16384 2013-01-05 01:43 lost+found

-rw-r--r-- 1 root root 3004323 2013-01-05 01:51

vmlinux-2.6.27.19-5-default.gz

(none):/home/liuzq/Desktop # md5sum

/mnt/u1/vmlinux-2.6.27.19-5-default.gz

71603654a26edc4faa85054cbe2900be

/mnt/u1/vmlinux-2.6.27.19-5-default.gz

(none):/home/liuzq/Desktop # pvs

PV VG Fmt Attr PSize PFree

/dev/sdb1 vg_test lvm2 a- 100.00G 85.00G

(none):/home/liuzq/Desktop # lvs

LV VG Attr LSize Origin Snap% Move Log Copy%

Convert

lvm_u1 vg_test -wi-ao 15.00G

删除LVM逻辑卷和组使用lvremove命令可以删除卷组里的LVM逻辑卷

(none):/home/liuzq/Desktop #lvremove /dev/ vg_test /lvm_u1

Do you really want to remove active logical volume "lvm_u1" ? [y/n]: y

Logical volume "lvm_u1" successfully removed

使用vgremove命令可以删除现有LVM卷组

(none):/home/liuzq/Desktop #vgremove vg_test

Volume group "vgusb" successfully removed