扩展KVM镜像的虚拟磁盘大小

当我们需要扩展模板镜像的虚拟磁盘大小时，比如原来的虚拟磁盘大小为20G，现在我们想将其扩展到30G，那么我们可以根据如下步骤来操作。

整个流程可以分为三个阶段：

1、扩展KVM镜像磁盘文件大小到30G。

2、扩展磁盘分区大小为30G。

3、扩展文件系统大小为30G。

假若当前有一个名为 test_extend.img 的模板镜像，其格式为 qcow2， virtual_size为 20G

1、首先可以使用qemu-img来查看该模板镜像的元信息：

root@cason:~/image# qemu-img info test_extend.img
image: test_extend.img
file format: qcow2
virtual size: 20G ( bytes)
disk size: 309M
cluster_size:
Format specific information:
    compat: 1.1
    lazy refcounts: false
root@cason:~/image# 

2、由于需要使用到qemu-nbd，因此我们需要先确认nbd模板已经被load：

root@cason:~/image# lsmod | grep nbd
root@cason:~/image#

执行如上命令发现没有任何输出，则表示当前系统并没有加载nbd模块

3、加载nbd模板，并再次确认（若没有nbd模块，则可以参考这里进行编译安装）：

root@cason:~/image# modprobe nbd max_part=
root@cason:~/image# lsmod | grep nbd
nbd
root@cason:~/image# 

此时nbd模板已经正常加载了

4、通过qemu-img命令来扩展虚拟磁盘的virtual_size为 30G：

root@cason:~/image# qemu-img resize test_extend.img
Image resized.
root@cason:~/image# qemu-img info test_extend.img
image: test_extend.img
file format: qcow2
virtual size: 30G ( bytes)
disk size: 309M
cluster_size:
Format specific information:
    compat: 1.1
    lazy refcounts: false
root@cason:~/image# 

5、下面通过qemu-nbd挂载test_extend.img到/dev/nbd0设备上：

root@cason:~/image# qemu-nbd -c /dev/nbd0 ./test_extend.img
root@cason:~/image# ll /dev/nbd* | grep nbd0
brw-rw----  root disk ,    11月  : /dev/nbd0
brw-rw----  root disk ,    11月  : /dev/nbd0p1
root@cason:~/image# 

挂载成功后，在/dev/下会看到如上信息，其中/dev/nbd0p1表示该虚拟磁盘仅有一个分区

6、下面开始通过fdisk来扩展虚拟磁盘分区大小：

root@cason:~/image# fdisk /dev/nbd0

Command (m for help): p

Disk /dev/nbd0: 32.2 GB,  bytes
 heads,  sectors/track,  cylinders, total  sectors
Units = sectors of  *  =  bytes
Sector size (logical/physical):  bytes /  bytes
I/O size (minimum/optimal):  bytes /  bytes
Disk identifier: 0x000e8e8d

     Device Boot      Start         End      Blocks   Id  System
/dev/nbd0p1   *                     Linux

Command (m for help): d
Selected partition 

Command (m for help): p

Disk /dev/nbd0: 32.2 GB,  bytes
 heads,  sectors/track,  cylinders, total  sectors
Units = sectors of  *  =  bytes
Sector size (logical/physical):  bytes /  bytes
I/O size (minimum/optimal):  bytes /  bytes
Disk identifier: 0x000e8e8d

     Device Boot      Start         End      Blocks   Id  System

Command (m for help): n
Partition type:
   p   primary ( primary,  extended,  free)
   e   extended
Select (default p): p
Partition number (-, default ):
Using default value
First sector (-, default ):
Using default value
Last sector, +sectors or +size{K,M,G} (-, default ):
Using default value 

Command (m for help): p

Disk /dev/nbd0: 32.2 GB,  bytes
 heads,  sectors/track,  cylinders, total  sectors
Units = sectors of  *  =  bytes
Sector size (logical/physical):  bytes /  bytes
I/O size (minimum/optimal):  bytes /  bytes
Disk identifier: 0x000e8e8d

     Device Boot      Start         End      Blocks   Id  System
/dev/nbd0p1                         Linux

Command (m for help): a
Partition number (-): 

Command (m for help): p

Disk /dev/nbd0: 32.2 GB,  bytes
 heads,  sectors/track,  cylinders, total  sectors
Units = sectors of  *  =  bytes
Sector size (logical/physical):  bytes /  bytes
I/O size (minimum/optimal):  bytes /  bytes
Disk identifier: 0x000e8e8d

     Device Boot      Start         End      Blocks   Id  System
/dev/nbd0p1   *                     Linux

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

Calling ioctl() to re-read partition table.
Syncing disks.
root@cason:~/image# 

如此以来，我们已经将该虚拟磁盘的分区大小扩展到了30G

7、至此，我们还需要将文件系统扩展到30G：

root@cason:~/image# e2fsck -fp /dev/nbd0p1
/dev/nbd0p1: Deleted inode  has zero dtime.  FIXED.
/dev/nbd0p1: / files (0.2% non-contiguous), / blocks

root@cason:~/image# resize2fs /dev/nbd0p1
resize2fs 1.42. (-Feb-)
Resizing the filesystem on /dev/nbd0p1 to  (4k) blocks.
The filesystem on /dev/nbd0p1 is now  blocks long.

root@cason:~/image# qemu-nbd -d /dev/nbd0
/dev/nbd0 disconnected

至此，我们就完成了扩展虚拟磁盘大小的操作。