Linux-一些必须掌握的命令（八）LVM逻辑卷

学习目标：

LVM逻辑卷管理器

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学习前言：

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。

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## 学习内容： 1、创建逻辑卷
2、扩容逻辑卷
3、缩小逻辑卷
4、逻辑卷快照
5、删除逻辑卷

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操作：

一、创建
步骤：让硬盘设备支持LVM技术（pvcreate）—硬盘设备加入到卷组(vgcreate)—切割一定空间作为逻辑卷(lvcreate)—创建成功的逻辑卷进行格式化然后挂载使用(mkfs、mount)

[root@lizhiqiang Desktop]# pvcreate /dev/sdc /dev/sdd   #支持
  Physical volume "/dev/sdc" successfully created
  Physical volume "/dev/sdd" successfully created
[root@lizhiqiang Desktop]# vgcreate aa /dev/sdc /dev/sdd    #加入到卷组
  Volume group "aa" successfully created
[root@lizhiqiang Desktop]# lvcreate -n bb -l 30 aa     #逻辑卷
  Logical volume "bb" created
[root@lizhiqiang Desktop]# lvdisplay        查看信息
 --- Logical volume ---
  LV Path                /dev/aa/bb
  LV Name                bb
  VG Name                aa
  LV UUID                qvOElL-qV5N-9V4V-ggFe-CqBm-hnaz-BK4Uij
  LV Write Access        read/write
  LV Creation host, time lizhiqiang, 2020-10-22 08:34:17 -0400
  LV Status              available
  # open                 0
  LV Size                120.00 MiB
  Current LE             30
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:2
[root@lizhiqiang Desktop]# mkfs.ext4 /dev/aa/bb      #格式化
[root@lizhiqiang Desktop]# mkdir -p /cc                #挂载所需目录
[root@lizhiqiang Desktop]# mount /dev/aa/bb /cc    #一次性挂载
[root@lizhiqiang Desktop]# echo "/dev/aa/bb /cc ext4 defaults 0 0" >> /etc/fstab   #挂载永久性挂载，/etc/fstab配置文件

二、扩容
扩容前，先卸载设备和挂载点的关联。
查看硬盘完整性
同步逻辑卷容量

[root@lizhiqiang Desktop]# umount /cc     卸载挂载
[root@lizhiqiang Desktop]# e2fsck -f /dev/aa/bb       查看硬盘完整性
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/aa/bb: 11/30720 files (9.1% non-contiguous), 9529/122880 blocks
[root@lizhiqiang Desktop]# resize2fs /dev/aa/bb       同步逻辑卷容量
resize2fs 1.42.9 (28-Dec-2013)
The filesystem is already 122880 blocks long.  Nothing to do!
[root@lizhiqiang Desktop]# lvextend -L 300M /dev/aa/bb     扩容逻辑卷  -L指定大小
  Extending logical volume bb to 300.00 MiB
  Logical volume bb successfully resized
[root@lizhiqiang Desktop]# mount /cc    挂载
[root@lizhiqiang Desktop]# df -h      查看
/dev/mapper/aa-bb                 287M  2.0M  266M   1% /cc

三、缩容
先卸载挂载
然后查看完整性
向系统报备一下即将要执行逻辑卷缩容的操作

[root@lizhiqiang Desktop]# umount /cc    卸载
[root@lizhiqiang Desktop]# e2fsck -f /dev/aa/bb      查看系统完整性
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/aa/bb: 11/77824 files (9.1% non-contiguous), 15979/307200 blocks
[root@lizhiqiang Desktop]# resize2fs /dev/aa/bb 150M     向系统报备一下即将要执行逻辑卷缩容
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/aa/bb to 153600 (1k) blocks.
The filesystem on /dev/aa/bb is now 153600 blocks long.

[root@lizhiqiang Desktop]# lvreduce -L 150M /dev/aa/bb      缩容指定到150M
  Rounding size to boundary between physical extents: 152.00 MiB
  WARNING: Reducing active logical volume to 152.00 MiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
  Do you really want to reduce bb? [y/n]: y       确认缩容这一步操作
  Reducing logical volume bb to 152.00 MiB
  Logical volume bb successfully resized
[root@lizhiqiang Desktop]# mount -a     挂载
[root@lizhiqiang Desktop]# df -h      查看挂载信息
pper/aa-bb                 142M  1.6M  130M   2% /cc

四、快照（注意：快照是一次性的）

[root@lizhiqiang Desktop]# echo " Hello " > /dyp/aa    往逻辑卷设备（dyp挂载的目录）写入一个文件
[root@lizhiqiang Desktop]# lvcreate -L 150M -s -n bb /dev/lzq/wn     为逻辑卷wn生成一个快照卷，命名为bb，指定切割大小为150M，快照卷和逻辑卷容量大小相等
  Rounding up size to full physical extent 152.00 MiB
  Logical volume "bb" created
[root@lizhiqiang Desktop]# dd if=/dev/zero of=/dyp/file bs=100M count=1    给逻辑卷dyp创建一个100M的名为mfile文件
1+0 records in
1+0 records out
104857600 bytes (105 MB) copied, 1.16478 s, 90.0 MB/s
[root@lizhiqiang Desktop]# lvdisplay 查看逻辑卷信息
截取了一部分
 --- Logical volume ---
  LV Path                /dev/lzq/bb
  LV Name                bb
  VG Name                lzq
  LV UUID                GidKVE-XgUQ-zaeG-CpBZ-EPeN-Zoaa-L7kPxZ
  LV Write Access        read/write
  LV Creation host, time lizhiqiang, 2020-10-23 05:50:54 -0400
  LV snapshot status     active destination for wn
  LV Status              available
  # open                 0
  LV Size                152.00 MiB
  Current LE             38
  COW-table size         152.00 MiB
  COW-table LE           38
  Allocated to snapshot  45.64%   占用率
  Snapshot chunk size    4.00 KiB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:3
[root@lizhiqiang Desktop]# umount /dyp   先卸载再恢复快照
[root@lizhiqiang Desktop]# lvconvert --merge /dev/lzq/bb   恢复快照（一次性）
  Merging of volume bb started.
  wn: Merged: 43.9%
  wn: Merged: 100.0%
  Merge of snapshot into logical volume wn has finished.
  Logical volume "bb" successfully removed
[root@lizhiqiang Desktop]# mount -a   挂载
[root@lizhiqiang Desktop]# ls /dyp   查看逻辑卷目录，可以发现创建快照后再创建的100M文件不见了，逻辑卷恢复成设置快照前的状态
aa  lost+found
[root@lizhiqiang Desktop]# cd /dyp
[root@lizhiqiang dyp]# cat aa   查看之前创建快照前的文件
 Hello 

五、删除逻辑卷

删除顺序与创建逻辑卷相反（逻辑卷-卷组-物理卷）

[root@lizhiqiang Desktop]# reboot  先重启
[root@lizhiqiang Desktop]# umount /dyp  卸载挂载
[root@lizhiqiang Desktop]# vim /etc/fstab   删除配置文件
[root@lizhiqiang Desktop]# lvremove /dev/lzq/wn  删除逻辑卷
Do you really want to remove active logical volume wn? [y/n]: y  确定删除
  Logical volume "wn" successfully removed
[root@lizhiqiang Desktop]# vgremove lzq   删除卷组
  Volume group "lzq" successfully removed
[root@lizhiqiang Desktop]# pvremove /dev/sd[c-d]  删除物理组（用的sdc与sdd）
  Labels on physical volume "/dev/sdc" successfully wiped
  Labels on physical volume "/dev/sdd" successfully wiped