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虚拟机镜像文件扩容

6 Jun 2019

虚拟机根据不同用途需要不同的容量大小。有时候它们是从同一个镜像文件克隆出来的，预设的容量是固定的，所以得想办法根据需要把镜像文件进行扩容。

扩容貌似很简单，但是真正做起来还是有些复杂的。

而且整个过程需要非常小心，先做备份以免处理不当导致数据丢失。

首先扩容镜像不是一步到位的，其中涉及了很多层，尤其是使用了 LVM 的情况。需要考虑以下几步：

  1. Image file
  2. LVM partition
  3. LVM physical volume
  4. LVM logical volume
  5. File system

除了第一步，其余的步骤对于真实物理磁盘也是一样处理的。

如果没有用到 LVM，3 和 4 可以跳过。

这里以 QCOW2 格式为例，其它格式都应该是类似的。

Resize the qcow2 image

Poweroff the virtual machine.

Check the size.

$ qemu-img info vm.qcow2
image: vm.qcow2
file format: qcow2
virtual size: 64G (68719476736 bytes)
disk size: 56G
cluster_size: 65536

Resize the image file.

$ qemu-img resize vm.qcow2 +960G
Image resized.

The new size.

$ qemu-img info vm.qcow2
image: vm.qcow2
file format: qcow2
virtual size: 1.0T (1099511627776 bytes)
disk size: 56G
cluster_size: 65536

Resize the partition

Start the virtual machine.

$ virsh start vm

Login and resize lvm group.

Please pay great attention because any mistakes will destroy the data.

$ sudo fdisk /dev/vda
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/vda: 14.0 GB, 13958643712 bytes
16 heads, 63 sectors/track, 27046 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c55ce

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           3        1018      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/vda2            1018       20806     9972736   8e  Linux LVM
Partition 2 does not end on cylinder boundary.

Command (m for help): d
Partition number (1-4): 2

Command (m for help): p

Disk /dev/vda: 14.0 GB, 13958643712 bytes
16 heads, 63 sectors/track, 27046 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c55ce

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           3        1018      512000   83  Linux
Partition 1 does not end on cylinder boundary.

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (1-27046, default 1): 1018
Last cylinder, +cylinders or +size{K,M,G} (1018-27046, default 27046):
Using default value 27046

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Changed system type of partition 2 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/vda: 14.0 GB, 13958643712 bytes
16 heads, 63 sectors/track, 27046 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c55ce

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *           3        1018      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/vda2            1018       27046    13118160   8e  Linux LVM

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

Reboot the virtual machine.

Resize the physical volume

$ sudo pvdisplay
$ sudo pvresize /dev/vda2
$ sudo pvdisplay

Resize the logical volume

$ sudo lvdisplay
$ sudo lvextend -L+960G /dev/centos/root
$ sudo lvdisplay

Grow the file system

Grow xfs partition.

$ sudo xfs_growfs /dev/centos/root

Different file system has different commands. Ext4 needs to use resize2fs.