一.背景：因为公司虚拟机 （/） 目录容量过小，导致一些任务不能正常执行，需要给虚拟机扩容
二.操作：
初始磁盘情况：
1.使用 df 命令查看磁盘与目录的容量：
[root@shaonian ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root 48G 22G 25G 47% /
tmpfs 3.8G 0 3.8G 0% /dev/shm
/dev/xvda1 485M 33M 427M 8% /boot
/dev/mapper/VolGroup-lv_home 4.7G 138M 4.4G 4% /home
cm_processes 3.8G 808K 3.8G 1% /var/run/cloudera-scm-agent/process
2.使用 fdisk -l 命令查看磁盘分区：
[root@shaonian ~]# fdisk -l
Disk /dev/xvdb: 85.9 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/xvda: 64.4 GB, 64424509440 bytes
255 heads, 63 sectors/track, 7832 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000e9377
Device Boot Start End Blocks Id System
/dev/xvda1 * 1 64 512000 83 Linux
Partition 1 does not end on cylinder boundary.
/dev/xvda2 64 7833 62401536 8e Linux LVM
Disk /dev/xvdd: 119 MB, 119891968 bytes
255 heads, 63 sectors/track, 14 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_root: 52.3 GB, 52344913920 bytes
255 heads, 63 sectors/track, 6363 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_swap: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_home: 5108 MB, 5108662272 bytes
255 heads, 63 sectors/track, 621 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
发现执行 fdisk -l 显示的第一行，显示出的 /dev/xvdb 分区，并没有被使用。这就是是管理人员分出给磁盘扩容用的磁盘空间，我们接下来要用这个分区为（/）目录扩容
3.接着执行 fdisk /dev/xvdb ，进入 fdisk 命令行给磁盘分区
[root@shaonian ~]# fdisk /dev/xvdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xd259beb1.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help): p
Disk /dev/xvdb: 85.9 GB, 85899345920 bytes
255 heads, 63 sectors/track, 10443 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xd259beb1
Device Boot Start End Blocks Id System
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-10443, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-10443, default 10443):
Using default value 10443
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
可以看出，输入fdisk /dev/xvdb 命令后，提示我们输入命令，我们依次输入以下命令：
p 查看已有分区，由于这个分区是新的，所以为空
n 新建分区：
p 新建主分区
1 输入分区号，因为之前没有分区，所以这是第一个分区，分区号为1
接下来 First cylinder 和 Last cylinder 我们直接点击回车，默认使用全部空间
t 改变分区类型
8e 改变分区类型为 LVM
w 写入改变
此时系统将改变分区，然后退出 fdisk 命令行。如果没有自动退出，输入 q 退出。
4. 用 mkfs 命令对分区进行格式化
mkfs -t ext3 /dev/xvdb1
此时将进入漫长的等待......
5.添加 LVM到原来的 LVM组
lvm 进入lvm管理
lvm> pvcreate /dev/xvdb1 创建虚拟分区
lvm> vgextend VolGroup /dev/xvdb1 把刚刚创建的分区添加到虚拟分区组
lvm>lvextend -L +79.5 /dev/mapper/VolGroup-lv_root 扩展容量（可以看到 /dev/mapper/VolGroup-lv_root）就是我们执行 df -h 时 （/）目录的文件系统）
lvm> quit 退出
6. 文件系统扩容
resize2fs /dev/mapper/VolGroup-lv_root
至此，扩容全部完成，此时再次执行 df -h :
[root@shaonian ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root 127G 22G 99G 18% /
tmpfs 3.8G 0 3.8G 0% /dev/shm
/dev/xvda1 485M 33M 427M 8% /boot
/dev/mapper/VolGroup-lv_home 4.7G 138M 4.4G 4% /home
cm_processes 3.8G 792K 3.8G 1% /var/run/cloudera-scm-agent/process
可以看到 （/）目录的容量大大增加了
PS:顺便一提，一共扩容了三台虚拟机，其中两台都是很顺利的，有一台不知道什么原因（可能是其中某一步操作错误），在执行
lvm> vgextend VolGroup /dev/mapper/Group-lv_root
操作时，出现了如下错误：
Couldn't find device with uuid cRdLUx-1ttO-JUKw-K2Bu-FOw2-EIrk-87Xdl3.
运行 pvscan 查看 pv：
lvm> pvscan
Couldn't find device with uuid cRdLUx-1ttO-JUKw-K2Bu-FOw2-EIrk-87Xdl3.
Couldn't find device with uuid 7Ef30A-6qRY-bBP0-CTH9-f6ut-kE8x-ch4c2j.
PV /dev/xvda2 VG VolGroup lvm2 [59.51 GiB / 0 free]
PV unknown device VG VolGroup lvm2 [80.00 GiB / 80.00 GiB free]
PV unknown device VG VolGroup lvm2 [80.00 GiB / 80.00 GiB free]
PV /dev/xvdb4 VG VolGroup lvm2 [80.00 GiB / 80.00 GiB free]
Total: 4 [299.50 GiB] / in use: 4 [299.50 GiB] / in no VG: 0 [0 ]
发现 有两行 出现了 unknown device
执行
lvm> vgreduce --removemissing VolGroup
即可。
原地址：https://www.cnblogs.com/dreamtecher/p/5840054.html