LVM，即Logical Volume Manager，區(qū)別于章文嵩博士創(chuàng)作的LVS（Linux Virtual Server）。前者用于磁盤分區(qū)管理，而后者是一款運行在四層的負(fù)載均衡軟件。

先說操作，再做介紹

新建、擴展和縮減LVM卷（常用）

操作場景：主機新增一塊硬盤，縮減/home目錄空間，擴展/目錄空間，為/usr新增分區(qū)

1. 新硬盤創(chuàng)建pv

[root@localhost ~]# pvcreate /dev/sdc 
  Physical volume "/dev/sdc" successfully created

2. 將pv加入的vg

[root@localhost ~]# vgextend VolGroup /dev/sdc 
  Volume group "VolGroup" successfully extended

3. 縮減/home空間
   縮減五步走：卸載分區(qū)—檢查分區(qū)—重設(shè)分區(qū)大小—縮減lv大小—掛載分區(qū)

[root@localhost ~]# umount /home

[root@localhost ~]# e2fsck -f /dev/VolGroup/lv_home 
e2fsck 1.41.12 (17-May-2010)
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/VolGroup/lv_home: 11/65280 files (0.0% non-contiguous), 8523/261120 blocks

[root@localhost ~]# resize2fs /dev/VolGroup/lv_home 200M
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/VolGroup/lv_home to 51200 (4k) blocks.
The filesystem on /dev/VolGroup/lv_home is now 51200 blocks long.

[root@localhost ~]# lvreduce -L 200M /dev/mapper/VolGroup-lv_home 
  WARNING: Reducing active logical volume to 200.00 MiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce VolGroup/lv_home? [y/n]: y
  Size of logical volume VolGroup/lv_home changed from 1020.00 MiB (255 extents) to 200.00 MiB (50 extents).
  Logical volume lv_home successfully resized.

[root@localhost ~]# mount /home

4. 擴展/目錄空間
   兩步走：擴展lv—重設(shè)分區(qū)大小

[root@localhost ~]# lvextend -L +800M /dev/VolGroup/lv_root 
  Size of logical volume VolGroup/lv_root changed from 8.51 GiB (2178 extents) to 9.29 GiB (2378 extents).
  Logical volume lv_root successfully resized.

[root@localhost ~]# resize2fs /dev/VolGroup/lv_root 
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/VolGroup/lv_root is mounted on /; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/VolGroup/lv_root to 2435072 (4k) blocks.
The filesystem on /dev/VolGroup/lv_root is now 2435072 blocks long.

5. 為/usr/test掛載新分區(qū)
   四步走：新建lv—格式化分區(qū)—修改/etc/fstab（保證操作系統(tǒng)開機能自動掛載分區(qū)）—掛載分區(qū)

[root@localhost ~]# lvcreate -l 100%free -n lv_usr_test VolGroup
  Logical volume "lv_usr_test" created.

[root@localhost ~]# mkfs.ext4 /dev/VolGroup/lv_usr_test 
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
66672 inodes, 266240 blocks
13312 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=272629760
9 block groups
32768 blocks per group, 32768 fragments per group
7408 inodes per group
Superblock backups stored on blocks: 
    32768, 98304, 163840, 229376
Writing inode tables: done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@localhost ~]# vi /etc/fstab 
#
# /etc/fstab
# Created by anaconda on Tue Apr 18 15:50:05 2017
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/VolGroup-lv_root /                       ext4    defaults        1 1
UUID=5f76841a-7d60-4da2-9db1-7c6356bc3812 /boot                   ext4    defaults        1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/mapper/VolGroup-lv_home /home                   ext4    defaults        0 0
/dev/mapper/VolGroup-lv_usr_test /usr/test                   ext4    defaults        0 0

[root@localhost ~]# mount /usr/test

此處應(yīng)該可以介紹一下LVM的原理了

LVM原理其實很簡單，LVM是為了解決傳統(tǒng)的物理分區(qū)難以擴展和更改的問題而產(chǎn)生的工具。LVM其實是在物理分區(qū)和掛載目錄之間插入一層，將傳統(tǒng)的物理分區(qū)—掛載目錄的模式改變?yōu)槲锢矸謪^(qū)（或磁盤）—PV—VG—LV—掛載目錄。

LVM模型

再圍繞上面的內(nèi)容扯點相關(guān)的

LVM的常用命令

pvcreate、vgcreate、lvcreate：pv、vg、lv創(chuàng)建
pvdisplay、vgdisplay、lvdisplaly：顯示pv、vg、lv詳細(xì)屬性信息
pvs、vgs、lvs：顯示pv、vg、lv使用情況
pvscan、vgscan、lvscan：查詢系統(tǒng)中所有pv、vg、lv
vgremove、lvremove：vg、lv刪除
vgextend、lvextend：擴展vg、lv大小
vgreduce、lvreduce：將pv從vg中刪除、縮減lv大小
pvmove：將一個pv中的數(shù)據(jù)轉(zhuǎn)移到另一個pv中
小知識點，上面命令涉及到大小時，-l后面跟pe（或le）數(shù)量或給定百分比（100%free表示使用全部可用空間），-L 后面跟容量（200M、2G等）。
至于上面這些命令具體參數(shù)，自己--help或者man一下好嗎

關(guān)于/etc/fstab

內(nèi)核在啟動過程中會讀取/etc/fstab文件中的配置來自動掛載磁盤。這樣將LVM創(chuàng)建的邏輯卷或物理磁盤分區(qū)的掛載信息寫入這個文件后我們就不需要每次開機之后手動掛載了。

[root@localhost ~]# cat /etc/fstab 
#
# /etc/fstab
# Created by anaconda on Tue Apr 18 15:50:05 2017
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/VolGroup-lv_root /                       ext4    defaults        1 1
UUID=5f76841a-7d60-4da2-9db1-7c6356bc3812 /boot                   ext4    defaults        1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/mapper/VolGroup-lv_home /home                   ext4    defaults        0 0

如上所示，此文件中的分區(qū)掛載信息有6列：

• 第一列：device，磁盤或者LVM分區(qū)的設(shè)備文件（label）或者UUID
• 第二列：Mount point，掛載點，就是要掛載的目錄
• 第三列：filesystem，磁盤文件系統(tǒng)的格式，如ext2、ext3、ext4等
• 第四列：parameters，文件系統(tǒng)參數(shù)

• 第五列和第六列：是否被dump命令備份和開機時是否用fsck檢驗文件系統(tǒng)完整性。0表示否，1表示是。