DM设备的创建与管理

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   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   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？？？？？）