RAID（独立冗余磁盘阵列）

RAID 0

RAID 1

RAID 5

RAID 10

部署磁盘阵列

mdadm命令的常用参数以及作用

参数	作用
-a	检测设备名称
-n	指定设备数量
-l	指定RAID级别
-C	创建
-v	显示过程
-f	模拟设备损坏
-r	移除设备
-Q	查看摘要信息
-D	查看详细信息
-S	停止RAID磁盘阵列

[root@localhost ~]# mdadm -Cv /dev/md0 -a yes -n 4 -l 10 /dev/sdb /dev/sdc /dev/sdd /dev/sde
mdadm: layout defaults to n2
mdadm: layout defaults to n2
mdadm: chunk size defaults to 512K
mdadm: size set to 20954112K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

把制作好的RAID磁盘阵列格式化为ext4格式

[root@localhost ~]# mkfs.ext4 /dev/md0
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
2621440 inodes, 10477056 blocks
523852 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2157969408
320 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, 2654208, 
    4096000, 7962624
Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

创建挂载点然后把硬盘设备进行挂载操作

[root@localhost ~]# mkdir /RAID
[root@localhost ~]# mount /dev/md0 /RAID/
[root@localhost ~]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   17G  1.1G   16G   7% /
devtmpfs                 898M     0  898M   0% /dev
tmpfs                    910M     0  910M   0% /dev/shm
tmpfs                    910M  9.6M  901M   2% /run
tmpfs                    910M     0  910M   0% /sys/fs/cgroup
/dev/sda1               1014M  146M  869M  15% /boot
tmpfs                    182M     0  182M   0% /run/user/0
/dev/md0                  40G   49M   38G   1% /RAID

查看/dev/md0磁盘阵列的详细信息，并把挂载信息写入到配置文件中，使其永久生效。

[root@localhost ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Mon Apr 15 17:43:04 2019
        Raid Level : raid10
        Array Size : 41908224 (39.97 GiB 42.91 GB)
     Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent
       Update Time : Mon Apr 15 17:44:14 2019
             State : active, resyncing 
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0
            Layout : near=2
        Chunk Size : 512K
Consistency Policy : resync
     Resync Status : 66% complete
              Name : localhost.localdomain:0  (local to host localhost.localdomain)
              UUID : 9b664b1c:ab2b2fb6:6a00adf6:6167ad51
            Events : 15
    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync set-A   /dev/sdb
       1       8       32        1      active sync set-B   /dev/sdc
       2       8       48        2      active sync set-A   /dev/sdd
       3       8       64        3      active sync set-B   /dev/sde
[root@localhost ~]# echo "/dev/md0 /RAID ext4 defaults 0 0" >> /etc/fstab

损坏磁盘阵列及修复

在确认有一块物理硬盘设备出现损坏而不能继续正常使用后，应该使用mdadm命令将其移除，然后查看RAID磁盘阵列的状态，可以发现状态已经改变。

[root@localhost ~]# mdadm /dev/md0 -f /dev/sdb
mdadm: set /dev/sdb faulty in /dev/md0
[root@localhost ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Apr 18 09:25:38 2019
        Raid Level : raid10
        Array Size : 41908224 (39.97 GiB 42.91 GB)
     Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent
       Update Time : Thu Apr 18 09:28:24 2019
             State : clean, degraded 
    Active Devices : 3
   Working Devices : 3
    Failed Devices : 1
     Spare Devices : 0
            Layout : near=2
        Chunk Size : 512K
Consistency Policy : resync
              Name : localhost.localdomain:0  (local to host localhost.localdomain)
              UUID : 09c273ff:77fa1bc2:84a934f1:b924fa6e
            Events : 27
    Number   Major   Minor   RaidDevice State
       -       0        0        0      removed
       1       8       32        1      active sync set-B   /dev/sdc
       2       8       48        2      active sync set-A   /dev/sdd
       3       8       64        3      active sync set-B   /dev/sde
       0       8       16        -      faulty   /dev/sdb

在RAID 10级别的磁盘阵列中，当RAID 1磁盘阵列中存在一个故障盘时并不影响RAID 10磁盘阵列的使用。当购买了新的硬盘设备后再使用mdadm命令来予以替换即可，在此期间我们可以在/RAID目录中正常地创建或删除文件。由于我们是在虚拟机中模拟硬盘，所以先重启系统，然后再把新的硬盘添加到RAID磁盘阵列中。

[root@localhost ~]# umount /RAID/
[root@localhost ~]# mdadm /dev/md0 -a /dev/sdb
mdadm: added /dev/sdb
[root@localhost ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Apr 18 09:25:38 2019
        Raid Level : raid10
        Array Size : 41908224 (39.97 GiB 42.91 GB)
     Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent
       Update Time : Thu Apr 18 09:34:14 2019
             State : clean, degraded, recovering 
    Active Devices : 3
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 1
            Layout : near=2
        Chunk Size : 512K
Consistency Policy : resync
    Rebuild Status : 30% complete
              Name : localhost.localdomain:0  (local to host localhost.localdomain)
              UUID : 09c273ff:77fa1bc2:84a934f1:b924fa6e
            Events : 47
    Number   Major   Minor   RaidDevice State
       4       8       16        0      spare rebuilding   /dev/sdb
       1       8       32        1      active sync set-B   /dev/sdc
       2       8       48        2      active sync set-A   /dev/sdd
       3       8       64        3      active sync set-B   /dev/sde
[root@localhost ~]# mount -a

磁盘阵列+备份盘

为了避免多个实验之间相互发生冲突，我们需要保证每个实验的相对独立性，为此需要大家自行将虚拟机还原到初始状态。
部署RAID 5磁盘阵列时，至少需要用到3块硬盘，还需要再加一块备份硬盘，所以总计需要在虚拟机中模拟4块硬盘设备

现在创建一个RAID 5磁盘阵列+备份盘。在下面的命令中，参数-n 3代表创建这个RAID 5磁盘阵列所需的硬盘数，参数-l 5代表RAID的级别，而参数-x 1则代表有一块备份盘。当查看/dev/md0（即RAID 5磁盘阵列的名称）磁盘阵列的时候就能看到有一块备份盘在等待中了。

[root@localhost ~]# mdadm -Cv /dev/md0 -n 3 -l 5 -x 1 /dev/sdb /dev/sdc /dev/sdd /dev/sde
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 512K
mdadm: /dev/sdb appears to be part of a raid array:
       level=raid10 devices=4 ctime=Thu Apr 18 09:25:38 2019
mdadm: /dev/sdc appears to be part of a raid array:
       level=raid10 devices=4 ctime=Thu Apr 18 09:25:38 2019
mdadm: /dev/sdd appears to be part of a raid array:
       level=raid10 devices=4 ctime=Thu Apr 18 09:25:38 2019
mdadm: /dev/sde appears to be part of a raid array:
       level=raid10 devices=4 ctime=Thu Apr 18 09:25:38 2019
mdadm: size set to 20954112K
Continue creating array? y           
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@localhost ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Apr 18 09:39:26 2019
        Raid Level : raid5
        Array Size : 41908224 (39.97 GiB 42.91 GB)
     Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
      Raid Devices : 3
     Total Devices : 4
       Persistence : Superblock is persistent
       Update Time : Thu Apr 18 09:40:28 2019
             State : clean 
    Active Devices : 3
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 1
            Layout : left-symmetric
        Chunk Size : 512K
Consistency Policy : resync
              Name : localhost.localdomain:0  (local to host localhost.localdomain)
              UUID : f72d4ba2:1460fae8:9f00ce1f:1fa2df5e
            Events : 18
    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       4       8       48        2      active sync   /dev/sdd
       3       8       64        -      spare   /dev/sde

将部署好的RAID 5磁盘阵列格式化为ext4文件格式，然后挂载到目录上，之后就可以使用了。

[root@localhost ~]# mkfs.ext4 /dev/md0
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
2621440 inodes, 10477056 blocks
523852 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2157969408
320 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, 2654208, 
    4096000, 7962624
Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   
[root@localhost ~]# echo "/dev/md0 /RAID ext4 defaults 0 0" >> /etc/fstab 
[root@localhost ~]# mkdir /RAID
[root@localhost ~]# mount -a

把硬盘设备/dev/sdb移出磁盘阵列，然后迅速查看/dev/md0磁盘阵列的状态

[root@localhost ~]# mdadm /dev/md0 -f /dev/sdb
mdadm: set /dev/sdb faulty in /dev/md0
[root@localhost ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Apr 18 09:39:26 2019
        Raid Level : raid5
        Array Size : 41908224 (39.97 GiB 42.91 GB)
     Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
      Raid Devices : 3
     Total Devices : 4
       Persistence : Superblock is persistent
       Update Time : Thu Apr 18 09:51:48 2019
             State : clean, degraded, recovering 
    Active Devices : 2
   Working Devices : 3
    Failed Devices : 1
     Spare Devices : 1
            Layout : left-symmetric
        Chunk Size : 512K
Consistency Policy : resync
    Rebuild Status : 40% complete
              Name : localhost.localdomain:0  (local to host localhost.localdomain)
              UUID : f72d4ba2:1460fae8:9f00ce1f:1fa2df5e
            Events : 26
    Number   Major   Minor   RaidDevice State
       3       8       64        0      spare rebuilding   /dev/sde
       1       8       32        1      active sync   /dev/sdc
       4       8       48        2      active sync   /dev/sdd
       0       8       16        -      faulty   /dev/sdb

LVM（逻辑卷管理器）

逻辑卷管理器是Linux系统用于对硬盘分区进行管理的一种机制，理论性较强，其创建初衷是为了解决硬盘设备在创建分区后不易修改分区大小的缺陷。尽管对传统的硬盘分区进行强制扩容或缩容从理论上来讲是可行的，但是却可能造成数据的丢失。而LVM技术是在硬盘分区和文件系统之间添加了一个逻辑层，它提供了一个抽象的卷组，可以把多块硬盘进行卷组合并。这样一来，用户不必关心物理硬盘设备的底层架构和布局，就可以实现对硬盘分区的动态调整。

物理卷处于LVM中的最底层，可以将其理解为物理硬盘、硬盘分区或者RAID磁盘阵列，这都可以。卷组建立在物理卷之上，一个卷组可以包含多个物理卷，而且在卷组创建之后也可以继续向其中添加新的物理卷。逻辑卷是用卷组中空闲的资源建立的，并且逻辑卷在建立后可以动态地扩展或缩小空间。这就是LVM的核心理念。

部署逻辑卷

常用的LVM部署命令

功能/命令	物理卷管理	卷组管理	逻辑卷管理
扫描	pvscan	vgscan	lvscan
建立	pvcreate	vgcreate	lvcreate
显示	pvdisplay	vgdisplay	lvdisplay
删除	pvremove	vgremove	lvremove
扩展		vgextend	lvextend
缩小		vgreduce	lvreduce

为了避免多个实验之间相互发生冲突，请大家自行将虚拟机还原到初始状态，并在虚拟机中添加两块新硬盘设备，然后开机
第1步：让新添加的两块硬盘设备支持LVM技术

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

第2步：把两块硬盘设备加入到storage卷组中，然后查看卷组的状态

[root@localhost ~]# vgcreate storage /dev/sdb /dev/sdc
  Volume group "storage" successfully created
[root@localhost ~]# vgdisplay
  --- Volume group ---
  VG Name               centos
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <19.00 GiB
  PE Size               4.00 MiB
  Total PE              4863
  Alloc PE / Size       4863 / <19.00 GiB
  Free  PE / Size       0 / 0   
  VG UUID               hXvPk7-ey0X-GUp1-NesK-9ty4-LVMc-6FUtwh
  --- Volume group ---
  VG Name               storage
  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               39.99 GiB
  PE Size               4.00 MiB
  Total PE              10238
  Alloc PE / Size       0 / 0   
  Free  PE / Size       10238 / 39.99 GiB
  VG UUID               R3Lgwt-YdRK-3Qhx-vzzt-P4gM-yxbZ-VbeojU

第3步：切割出一个约为150MB的逻辑卷设备。
这里需要注意切割单位的问题。在对逻辑卷进行切割时有两种计量单位。
第一种是以容量为单位，所使用的参数为-L。例如，使用-L 150M生成一个大小为150MB的逻辑卷。
另外一种是以基本单元的个数为单位，所使用的参数为-l。每个基本单元的大小默认为4MB。例如，使用-l 37可以生成一个大小为37×4MB=148MB的逻辑卷。

[root@localhost ~]# lvcreate -n vo -l 37 storage
  Logical volume "vo" created.
[root@localhost ~]# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/centos/swap
  LV Name                swap
  VG Name                centos
  LV UUID                RHOW0p-W5MW-lfGs-rIFk-tcmK-bKsd-bdh3ej
  LV Write Access        read/write
  LV Creation host, time localhost, 2019-04-15 17:30:59 +0800
  LV Status              available
  # open                 2
  LV Size                2.00 GiB
  Current LE             512
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:1
  --- Logical volume ---
  LV Path                /dev/centos/root
  LV Name                root
  VG Name                centos
  LV UUID                u4rM0M-cE5q-ii2n-j7Bd-eXvd-Gsw0-8ByOgp
  LV Write Access        read/write
  LV Creation host, time localhost, 2019-04-15 17:31:00 +0800
  LV Status              available
  # open                 1
  LV Size                <17.00 GiB
  Current LE             4351
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:0
  --- Logical volume ---
  LV Path                /dev/storage/vo
  LV Name                vo
  VG Name                storage
  LV UUID                WP06I4-XA8u-mGqT-uFEZ-uhyN-nbrT-ehKMTe
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2019-04-18 13:37:34 +0800
  LV Status              available
  # open                 0
  LV Size                148.00 MiB
  Current LE             37
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:2

第4步：把生成好的逻辑卷进行格式化，然后挂载使用。

[root@localhost ~]# mkfs.ext4 /dev/storage/vo
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
38000 inodes, 151552 blocks
7577 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=33816576
19 block groups
8192 blocks per group, 8192 fragments per group
2000 inodes per group
Superblock backups stored on blocks: 
    8193, 24577, 40961, 57345, 73729
Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done 
[root@localhost ~]# mkdir /vo
[root@localhost ~]# mount /dev/storage/vo /vo
[root@localhost ~]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   17G 1003M   17G   6% /
devtmpfs                 898M     0  898M   0% /dev
tmpfs                    910M     0  910M   0% /dev/shm
tmpfs                    910M  9.5M  901M   2% /run
tmpfs                    910M     0  910M   0% /sys/fs/cgroup
/dev/sda1               1014M  146M  869M  15% /boot
tmpfs                    182M     0  182M   0% /run/user/0
/dev/mapper/storage-vo   140M  1.6M  128M   2% /vo
[root@localhost ~]# echo "/dev/storage/vo /vo ext4 defaults 0 0" >> /etc/fstab

扩容逻辑卷

第1步：把上一个实验中的逻辑卷vo扩展至290MB

[root@localhost ~]# umount /vo
[root@localhost ~]# lvextend -L 290M /dev/storage/vo 
  Rounding size to boundary between physical extents: 292.00 MiB.
  Size of logical volume storage/vo changed from 148.00 MiB (37 extents) to 292.00 MiB (73 extents).
  Logical volume storage/vo successfully resized.

第2步：检查硬盘完整性，并重置硬盘容量

[root@localhost ~]# e2fsck -f /dev/storage/vo
e2fsck 1.42.9 (28-Dec-2013)
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/storage/vo: 11/38000 files (0.0% non-contiguous), 10453/151552 blocks
[root@localhost ~]# resize2fs /dev/storage/vo
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/storage/vo to 299008 (1k) blocks.
The filesystem on /dev/storage/vo is now 299008 blocks long.

第3步：重新挂载硬盘设备并查看挂载状态

[root@localhost ~]# mount -a
[root@localhost ~]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   17G 1003M   17G   6% /
devtmpfs                 898M     0  898M   0% /dev
tmpfs                    910M     0  910M   0% /dev/shm
tmpfs                    910M  9.5M  901M   2% /run
tmpfs                    910M     0  910M   0% /sys/fs/cgroup
/dev/sda1               1014M  146M  869M  15% /boot
tmpfs                    182M     0  182M   0% /run/user/0
/dev/mapper/storage-vo   279M  2.1M  259M   1% /vo

缩小逻辑卷

第1步：检查文件系统的完整性

[root@localhost ~]# umount /vo
[root@localhost ~]# e2fsck -f /dev/storage/vo
e2fsck 1.42.9 (28-Dec-2013)
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/storage/vo: 11/74000 files (0.0% non-contiguous), 15507/299008 blocks

第2步：把逻辑卷vo的容量减小到120MB

[root@localhost ~]# resize2fs /dev/storage/vo 120M
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/storage/vo to 122880 (1k) blocks.
The filesystem on /dev/storage/vo is now 122880 blocks long.
[root@localhost ~]# lvreduce -L 120M /dev/storage/vo
  WARNING: Reducing active logical volume to 120.00 MiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce storage/vo? [y/n]: y
  Size of logical volume storage/vo changed from 292.00 MiB (73 extents) to 120.00 MiB (30 extents).
  Logical volume storage/vo successfully resized.

第3步：重新挂载文件系统并查看系统状态

[root@localhost ~]# mount -a
[root@localhost ~]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   17G 1003M   17G   6% /
devtmpfs                 898M     0  898M   0% /dev
tmpfs                    910M     0  910M   0% /dev/shm
tmpfs                    910M  9.5M  901M   2% /run
tmpfs                    910M     0  910M   0% /sys/fs/cgroup
/dev/sda1               1014M  146M  869M  15% /boot
tmpfs                    182M     0  182M   0% /run/user/0
/dev/mapper/storage-vo   113M  1.6M  103M   2% /vo

逻辑卷快照

LVM还具备有“快照卷”功能，该功能类似于虚拟机软件的还原时间点功能。例如，可以对某一个逻辑卷设备做一次快照，如果日后发现数据被改错了，就可以利用之前做好的快照卷进行覆盖还原。LVM的快照卷功能有两个特点：

快照卷的容量必须等同于逻辑卷的容量；
快照卷仅一次有效，一旦执行还原操作后则会被立即自动删除。

[root@localhost ~]# vgdisplay 
  --- Volume group ---
  VG Name               storage
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  4
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               39.99 GiB
  PE Size               4.00 MiB
  Total PE              10238
  Alloc PE / Size       30 / 120.00 MiB
  Free  PE / Size       10208 / <39.88 GiB        //容量剩余39.88G
  VG UUID               R3Lgwt-YdRK-3Qhx-vzzt-P4gM-yxbZ-VbeojU

接下来用重定向往逻辑卷设备所挂载的目录中写入一个文件

[root@localhost ~]# echo "hello world" > /vo/readme.txt
[root@localhost ~]# ls -l /vo
total 14
drwx------. 2 root root 12288 Apr 18 13:38 lost+found
-rw-r--r--. 1 root root    12 Apr 18 13:48 readme.txt

第1步：使用-s参数生成一个快照卷，使用-L参数指定切割的大小。
另外，还需要在命令后面写上是针对哪个逻辑卷执行的快照操作。

[root@localhost ~]# lvcreate -L 120M -s -n SNAP /dev/storage/vo
  Logical volume "SNAP" created.
[root@localhost ~]# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/storage/vo
  LV Name                vo
  VG Name                storage
  LV UUID                WP06I4-XA8u-mGqT-uFEZ-uhyN-nbrT-ehKMTe
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2019-04-18 13:37:34 +0800
  LV snapshot status     source of
                         SNAP [active]
  LV Status              available
  # open                 1
  LV Size                120.00 MiB
  Current LE             30
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:2
  --- Logical volume ---
  LV Path                /dev/storage/SNAP
  LV Name                SNAP
  VG Name                storage
  LV UUID                WUhSh5-GVZx-VNs5-ChOd-2EKo-50Pj-N5VDFH
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2019-04-18 13:50:24 +0800
  LV snapshot status     active destination for vo
  LV Status              available
  # open                 0
  LV Size                120.00 MiB
  Current LE             30
  COW-table size         120.00 MiB
  COW-table LE           30
  Allocated to snapshot  0.01%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:5

第2步：在逻辑卷所挂载的目录中创建一个100MB的垃圾文件，然后再查看快照卷的状态。可以发现存储空间占的用量上升了

[root@localhost ~]# dd if=/dev/zero of=/vo/files count=1 bs=100M
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 3.29409 s, 31.8 MB/s
[root@localhost ~]# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/storage/vo
  LV Name                vo
  VG Name                storage
  LV UUID                WP06I4-XA8u-mGqT-uFEZ-uhyN-nbrT-ehKMTe
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2019-04-18 13:37:34 +0800
  LV snapshot status     source of
                         SNAP [active]
  LV Status              available
  # open                 1
  LV Size                120.00 MiB
  Current LE             30
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:2
  --- Logical volume ---
  LV Path                /dev/storage/SNAP
  LV Name                SNAP
  VG Name                storage
  LV UUID                WUhSh5-GVZx-VNs5-ChOd-2EKo-50Pj-N5VDFH
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2019-04-18 13:50:24 +0800
  LV snapshot status     active destination for vo
  LV Status              available
  # open                 0
  LV Size                120.00 MiB
  Current LE             30
  COW-table size         120.00 MiB
  COW-table LE           30
  Allocated to snapshot  83.71%
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:5

第3步：为了校验SNAP快照卷的效果，需要对逻辑卷进行快照还原操作。在此之前记得先卸载掉逻辑卷设备与目录的挂载。

[root@localhost ~]# umount /vo
[root@localhost ~]# lvconvert --merge /dev/storage/SNAP 
  Merging of volume storage/SNAP started.
  storage/vo: Merged: 31.39%
  storage/vo: Merged: 100.00%

第4步：快照卷会被自动删除掉，并且刚刚在逻辑卷设备被执行快照操作后再创建出来的100MB的垃圾文件也被清除了

[root@localhost ~]# mount -a
[root@localhost ~]# ls /vo/
lost+found  readme.txt

删除逻辑卷

第1步：取消逻辑卷与目录的挂载关联，删除配置文件中永久生效的设备参数。

[root@localhost ~]# umount /vo/
[root@localhost ~]# vi /etc/fstab 
#
# /etc/fstab
# Created by anaconda on Mon Apr 15 17:31:00 2019
#
# 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/centos-root /                       xfs     defaults        0 0
UUID=63e91158-e754-41c3-b35d-7b9698e71355 /boot                   xfs     defaults        0 0
/dev/mapper/centos-swap swap                    swap    defaults        0 0

第2步：删除逻辑卷设备，需要输入y来确认操作

[root@localhost ~]# lvremove /dev/storage/vo 
Do you really want to remove active logical volume storage/vo? [y/n]: y
  Logical volume "vo" successfully removed

第3步：删除卷组，此处只写卷组名称即可，不需要设备的绝对路径。

[root@localhost ~]# vgremove storage
  Volume group "storage" successfully removed

第4步：删除物理卷设备

[root@localhost ~]# pvremove /dev/sdb /dev/sdc
  Labels on physical volume "/dev/sdb" successfully wiped.
  Labels on physical volume "/dev/sdc" successfully wiped.

使用RAID与LVM磁盘阵列技术