DM（Device Mapper）即设备映射(逻辑设备)。
MD和DM是Linux内核上2种工作机制(实现逻辑设备)不同的模块。
Physical Volume(PV): 物理卷 底层
Volume Group(VG): 卷组 中间层
Logical Volume(LV)：逻辑卷 第一层(可伸缩)
Physical Extend(PE)：物理盘区 类似于RAID的chunk
Logical Extend(LE)：逻辑盘区 PE在逻辑卷层面上的称谓
各层的管理命令：
pv
pvcreate, pvremove, pvmove, pvdisplay, pvs, pvscan
vg
vgcreate, vgremove, vgextend, vgreduce, vgdisplay, pvs, vgscan
lv
lvcreate, lvremove, lvextend, lvreduce, lvresize, lvdisplay, lvs,lvscan
以下是实现过程（10G的卷组）：
1、创建Linux LVM分区
[root@ant-colonies ~]# fdisk /dev/sda
...
Command (m for help): t
Partition number (1-13): 13
Hex code (type L to list codes): 8e
Changed system type of partition 13 to 8e (Linux LVM)
...
/dev/sda11 4210 4602 3156741 8e Linux LVM
/dev/sda12 4603 5517 7349706 8e Linux LVM
/dev/sda13 5518 6171 5253223+ 8e Linux LVM
[root@ant-colonies ~]# cat /proc/partitions
major minor #blocks name
...
8 11 3156741 sda11
8 12 7349706 sda12
8 13 5253223 sda13
2、创建物理卷（Physical Volume）
[root@ant-colonies ~]# pvcreate /dev/sda{11,12}
Physical volume "/dev/sda11" successfully created
Physical volume "/dev/sda12" successfully created
[root@ant-colonies ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda11 lvm2 --- 3.01g 3.01g
/dev/sda12 lvm2 --- 7.01g 7.01g
/dev/sda6 myvg lvm2 a-- 7.01g 6.95g
/dev/sda7 myvg lvm2 a-- 5.01g 5.01g
[root@ant-colonies ~]# pvdisplay
...
"/dev/sda11" is a new physical volume of "3.01 GiB"
--- NEW Physical volume ---
PV Name /dev/sda11
VG Name
PV Size 3.01 GiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID D0KinO-K7pw-rkIh-GsY1-dxDZ-d1MO-zBfjMZ
"/dev/sda12" is a new physical volume of "7.01 GiB"
--- NEW Physical volume ---
PV Name /dev/sda12
VG Name
PV Size 7.01 GiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID XJRRp1-awM3-qfDW-Qv46-ho2i-MS45-PmcxzG
[root@ant-colonies ~]# pvscan
PV /dev/sda6 VG myvg lvm2 [7.01 GiB / 6.95 GiB free]
PV /dev/sda7 VG myvg lvm2 [5.01 GiB / 5.01 GiB free]
PV /dev/sda11 lvm2 [3.01 GiB]
PV /dev/sda12 lvm2 [7.01 GiB]
Total: 4 [22.04 GiB] / in use: 2 [12.02 GiB] / in no VG: 2 [10.02 GiB]
3、创建卷组（Volume Group）
[root@ant-colonies ~]# vgs
VG #PV #LV #SN Attr VSize VFree
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies ~]# vgcreate MYVG /dev/sda{11,12}
Volume group "MYVG" successfully created
[root@ant-colonies ~]# vgs
VG #PV #LV #SN Attr VSize VFree
MYVG 2 0 0 wz--n- 10.02g 10.02g
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies ~]# vgdisplay MYVG
--- Volume group ---
VG Name MYVG
System ID
Format lvm2
Metadata Areas 2
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 2
Act PV 2
VG Size 10.02 GiB
PE Size 4.00 MiB
Total PE 2564
Alloc PE / Size 0 / 0
Free PE / Size 2564 / 10.02 GiB
VG UUID 8mp6sm-1Wj4-p82x-d7LG-OWSt-8i2q-BZmGKA
4、删除卷组创建指定PE大小的卷组
[root@ant-colonies ~]# vgremove MYVG
Volume group "MYVG" successfully removed
[root@ant-colonies ~]# vgcreate -s 8M MYVG /dev/sda{11,12}
Volume group "MYVG" successfully created
[root@ant-colonies ~]# vgdisplay MYVG
--- Volume group ---
VG Name MYVG
System ID
Format lvm2
Metadata Areas 2
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 2
Act PV 2
VG Size 10.02 GiB
PE Size 8.00 MiB
Total PE 1282
Alloc PE / Size 0 / 0
Free PE / Size 1282 / 10.02 GiB
VG UUID RI4sJU-OI6d-CSva-HBes-gfzP-MMu8-E2QPWu
5、移除物理卷成员“三部曲”
[root@ant-colonies ~]# vgs
VG #PV #LV #SN Attr VSize VFree
MYVG 2 0 0 wz--n- 10.02g 10.02g
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda11 MYVG lvm2 a-- 3.01g 3.01g
/dev/sda12 MYVG lvm2 a-- 7.01g 7.01g
/dev/sda6 myvg lvm2 a-- 7.01g 6.95g
/dev/sda7 myvg lvm2 a-- 5.01g 5.01g
1）将要移除的物理卷/dev/sda11的数据移动到同组其他物理卷
[root@ant-colonies ~]# pvmove /dev/sda11
No data to move for MYVG
2）将/dev/sda11从卷组中移除
[root@ant-colonies ~]# vgreduce MYVG /dev/sda11
Removed "/dev/sda11" from volume group "MYVG"
[root@ant-colonies ~]# vgs
VG #PV #LV #SN Attr VSize VFree
MYVG 1 0 0 wz--n- 7.01g 7.01g
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda11 lvm2 --- 3.01g 3.01g
/dev/sda12 MYVG lvm2 a-- 7.01g 7.01g
/dev/sda6 myvg lvm2 a-- 7.01g 6.95g
/dev/sda7 myvg lvm2 a-- 5.01g 5.01g
3）将物理卷/dev/sda11移除
[root@ant-colonies ~]# pvremove /dev/sda11
Labels on physical volume "/dev/sda11" successfully wiped
[root@ant-colonies ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda12 MYVG lvm2 a-- 7.01g 7.01g
/dev/sda6 myvg lvm2 a-- 7.01g 6.95g
/dev/sda7 myvg lvm2 a-- 5.01g 5.01g
6、添加新的物理卷到卷组
[root@ant-colonies ~]# pvcreate /dev/sda13
Physical volume "/dev/sda13" successfully created
[root@ant-colonies ~]# vgextend MYVG /dev/sda13
Volume group "MYVG" successfully extended
[root@ant-colonies ~]# vgs
VG #PV #LV #SN Attr VSize VFree
MYVG 2 0 0 wz--n- 12.02g 12.02g
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies ~]# pvdisplay /dev/sda13
--- Physical volume ---
PV Name /dev/sda13
VG Name MYVG
PV Size 5.01 GiB / not usable 2.10 MiB
Allocatable yes
PE Size 8.00 MiB #与卷组的PE大小一致
Total PE 641
Free PE 641
Allocated PE 0
PV UUID DJyRRk-NnZb-dqHt-pqUy-T83d-SkQO-e4S4U2
7、创建逻辑卷（Logical Volume）
[root@ant-colonies ~]# lvcreate -L 50M -n TESTLV MYVG
Rounding up size to full physical extent 56.00 MiB
Logical volume "TESTLV" created.
[root@ant-colonies ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
TESTLV MYVG -wi-a----- 56.00m
testlv myvg -wi-a----- 56.00m
[root@ant-colonies ~]# lvdisplay
--- Logical volume ---
LV Path /dev/MYVG/TESTLV
LV Name TESTLV
VG Name MYVG
LV UUID r41vKB-XplG-PCwV-q8C4-gaAT-Rxh1-ydSQFh
LV Write Access read/write
LV Creation host, time ant-colonies, 2017-01-20 18:15:31 +0800
LV Status available
# open 0
LV Size 56.00 MiB
Current LE 7
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:1
...
8、格式化
[root@ant-colonies ~]# mke2fs -j /dev/MYVG/TESTLV
...
9、挂载
[root@ant-colonies ~]# mount /dev/MYVG/TESTLV /user
[root@ant-colonies ~]# cp /etc/inittab /user
[root@ant-colonies ~]# cd /user
[root@ant-colonies user]# ls -l
total 14
-rw-r--r--. 1 root root 884 Jan 21 00:03 inittab
drwx------. 2 root root 12288 Jan 20 23:12 lost+found
[root@ant-colonies user]# mount
/dev/sda2 on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw,rootcontext="system_u:object_r:tmpfs_t:s0")
/dev/sda1 on /boot type ext4 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
/dev/mapper/MYVG-TESTLV on /user type ext3 (rw)
说明/dev/mapper/MYVG-TESTLV 和 /dev/MYVG/TESTLV均为/dev/dm-1的字符链接。
10、卸载
[root@ant-colonies user]# lvremove /dev/mapper/MYVG-TESTLV
Logical volume MYVG/TESTLV contains a filesystem in use.
[root@ant-colonies /]# umount /user
[root@ant-colonies /]# lvremove /dev/mapper/MYVG-TESTLV
Do you really want to remove active logical volume TESTLV? [y/n]: y
Logical volume "TESTLV" successfully removed # 意味着数据也被删除
[root@ant-colonies ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
testlv myvg -wi-a----- 56.00m
再次创建、格式化并挂载逻辑卷
[root@ant-colonies ~]# lvcreate -L 50M -n TESTLV MYVG
[root@ant-colonies ~]# mke2fs -j -b 4096 -E stride=16 /dev/mapper/MYVG-TESTLV
...
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=16 blocks, Stripe width=0 blocks
14336 inodes, 14336 blocks
...
[root@ant-colonies ~]# mount /dev/mapper/MYVG-TESTLV /user
[root@ant-colonies ~]# ls -l /user
total 16
drwx------. 2 root root 16384 Jan 21 00:24 lost+found
[root@ant-colonies ~]# cp /etc/inittab /user
[root@ant-colonies ~]# cd /user
[root@ant-colonies user]# ls -l
total 24
-rw-r--r--. 1 root root 884 Jan 21 00:29 inittab
drwx------. 2 root root 16384 Jan 21 00:24 lost+found
11、扩展逻辑卷
[root@ant-colonies user]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda12 MYVG lvm2 a-- 7.01g 6.95g
/dev/sda13 MYVG lvm2 a-- 5.01g 5.01g
/dev/sda6 myvg lvm2 a-- 7.01g 6.95g
/dev/sda7 myvg lvm2 a-- 5.01g 5.01g
[root@ant-colonies user]# vgs
VG #PV #LV #SN Attr VSize VFree
MYVG 2 1 0 wz--n- 12.02g 11.96g
myvg 2 1 0 wz--n- 12.02g 11.96g
[root@ant-colonies user]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
TESTLV MYVG -wi-ao---- 56.00m
testlv myvg -wi-a----- 56.00m
[root@ant-colonies user]# lvextend -L 5G /dev/mapper/MYVG-TESTLV
Size of logical volume MYVG/TESTLV changed from 56.00 MiB (7 extents) to 5.00 GiB (640 extents).
Logical volume TESTLV successfully resized
[root@ant-colonies user]# resize2fs -p /dev/mapper/MYVG-TESTLV
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/MYVG-TESTLV is mounted on /user; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/mapper/MYVG-TESTLV to 1310720 (4k) blocks.
The filesystem on /dev/mapper/MYVG-TESTLV is now 1310720 blocks long.
[root@ant-colonies user]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
TESTLV MYVG -wi-ao---- 5.00g
testlv myvg -wi-a----- 56.00m
[root@ant-colonies user]# ls -l
total 24
-rw-r--r--. 1 root root 884 Jan 21 00:29 inittab
drwx------. 2 root root 16384 Jan 21 00:24 lost+found
12、缩减逻辑卷（至2G）
[root@ant-colonies ~]# df -Ph # 查看逻辑卷大小
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 9.8G 2.1G 7.2G 23% /
tmpfs 491M 0 491M 0% /dev/shm
/dev/sda1 190M 36M 145M 20% /boot
/dev/mapper/MYVG-TESTLV 5.0G 4.2M 4.7G 1% /user
[root@ant-colonies ~]# umount /user # 卸载
[root@ant-colonies ~]# e2fsck -f /dev/mapper/MYVG-TESTLV # 强行检查逻辑卷
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/mapper/MYVG-TESTLV: 12/573440 files (0.0% non-contiguous), 19073/1310720 blocks
[root@ant-colonies ~]# resize2fs /dev/mapper/MYVG-TESTLV 2G
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/mapper/MYVG-TESTLV to 524288 (4k) blocks.
The filesystem on /dev/mapper/MYVG-TESTLV is now 524288 blocks long.
[root@ant-colonies ~]# lvreduce -L -3G /dev/mapper/MYVG-TESTLV
WARNING: Reducing active logical volume to 2.00 GiB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce TESTLV? [y/n]: y
Size of logical volume MYVG/TESTLV changed from 5.00 GiB (640 extents) to 2.00 GiB (256 extents).
Logical volume TESTLV successfully resized
[root@ant-colonies ~]# mount /dev/mapper/MYVG-TESTLV /user
[root@ant-colonies ~]# cd /user
[root@ant-colonies user]# ls -l
total 24
-rw-r--r--. 1 root root 884 Jan 21 00:29 inittab #文件未发生改变
drwx------. 2 root root 16384 Jan 21 00:24 lost+found
13、创建快照
[root@ant-colonies user]# lvcreate -L 50M -n TESTLV-SNAP -s -p r /dev/mapper/MYVG-TESTLV
Rounding up size to full physical extent 56.00 MiB
Logical volume "TESTLV-SNAP" created.
[root@ant-colonies user]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
TESTLV MYVG owi-aos--- 2.00g
TESTLV-SNAP MYVG sri-a-s--- 56.00m TESTLV 0.02
testlv myvg -wi-a----- 56.00m
[root@ant-colonies user]# mount /dev/mapper/MYVG-TESTLV /mnt
[root@ant-colonies user]# cd /mnt
[root@ant-colonies mnt]# ls -l
total 24
-rw-r--r--. 1 root root 884 Jan 21 00:29 inittab
drwx------. 2 root root 16384 Jan 21 00:24 lost+found
[root@ant-colonies mnt]# wc -l inittab
26 inittab
[root@ant-colonies mnt]# （之后的操作，在系统中修改数据，快照也发生改变，原因不明？？？？？）