抽空学学KVM（六）qemu-img命令使用

通过KVM创建虚拟机，用到的命令不多，而且可以通过qemu-img -help查看到非常详细的解释，常用的主要有以下几种：

1、qemu-img info  查看磁盘信息     #info [-f fmt] [--output=ofmt] [--backing-chain] filename

[root@KVM03-10 opt]# qemu-img info  centos2.1.raw
image: centos2.1.raw
file format: raw
virtual size: 10G (10737418240 bytes)
disk size: 1.2G

磁盘文件类型：

RAW：裸格式，连续，不支持快照等高级功能，但性能优异；

qcow2：支持快照，非连续，性能较好，qcow2，q=qemu，cow=copy on write 写时复制，写多少内容，占用多少磁盘空间

 

2、qemu-img create 创建磁盘         #create [-q] [-f fmt] [-o options] filename [size]

[root@KVM03-10 opt]# qemu-img --help
qemu-img version 1.5.3, Copyright (c) 2004-2008 Fabrice Bellard
usage: qemu-img command [command options]
QEMU disk image utility

Command syntax:
  check [-q] [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache] filename
  create [-q] [-f fmt] [-o options] filename [size]
  commit [-q] [-f fmt] [-t cache] filename
  compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] filename1 filename2
  convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-o options] [-s snapshot_name] [-S sparse_size] filename [filename2 [...]] output_filename
  info [-f fmt] [--output=ofmt] [--backing-chain] filename
  map [-f fmt] [--output=ofmt] filename
  snapshot [-q] [-l | -a snapshot | -c snapshot | -d snapshot] filename
  rebase [-q] [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b backing_file [-F backing_fmt] filename
  resize [-q] filename [+ | -]size
  amend [-q] [-f fmt] [-t cache] -o options filename

Command parameters:
  'filename' is a disk image filename
  'fmt' is the disk image format. It is guessed automatically in most cases
  'cache' is the cache mode used to write the output disk image, the valid
    options are: 'none', 'writeback' (default, except for convert), 'writethrough',
    'directsync' and 'unsafe' (default for convert)
  'src_cache' is the cache mode used to read input disk images, the valid
    options are the same as for the 'cache' option
  'size' is the disk image size in bytes. Optional suffixes
    'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M),
    'T' (terabyte, 1024G), 'P' (petabyte, 1024T) and 'E' (exabyte, 1024P)  are
    supported. 'b' is ignored.
  'output_filename' is the destination disk image filename
  'output_fmt' is the destination format
  'options' is a comma separated list of format specific options in a
    name=value format. Use -o ? for an overview of the options supported by the
    used format
  '-c' indicates that target image must be compressed (qcow format only)
  '-u' enables unsafe rebasing. It is assumed that old and new backing file
       match exactly. The image doesn't need a working backing file before
       rebasing in this case (useful for renaming the backing file)
  '-h' with or without a command shows this help and lists the supported formats
  '-p' show progress of command (only certain commands)
  '-q' use Quiet mode - do not print any output (except errors)
  '-S' indicates the consecutive number of bytes (defaults to 4k) that must
       contain only zeros for qemu-img to create a sparse image during
       conversion. If the number of bytes is 0, the source will not be scanned for
       unallocated or zero sectors, and the destination image will always be
       fully allocated
  '--output' takes the format in which the output must be done (human or json)
  '-n' skips the target volume creation (useful if the volume is created
       prior to running qemu-img)

Parameters to check subcommand:
  '-r' tries to repair any inconsistencies that are found during the check.
       '-r leaks' repairs only cluster leaks, whereas '-r all' fixes all
       kinds of errors, with a higher risk of choosing the wrong fix or
       hiding corruption that has already occurred.

Parameters to snapshot subcommand:
  'snapshot' is the name of the snapshot to create, apply or delete
  '-a' applies a snapshot (revert disk to saved state)
  '-c' creates a snapshot
  '-d' deletes a snapshot
  '-l' lists all snapshots in the given image

Parameters to compare subcommand:
  '-f' first image format
  '-F' second image format
  '-s' run in Strict mode - fail on different image size or sector allocation

Supported formats: vvfat vpc vmdk vhdx vdi ssh sheepdog rbd raw host_cdrom host_floppy host_device file qed qcow2 qcow parallels nbd iscsi gluster dmg tftp ftps ftp https http cloop bochs blkverify blkdebug

 [root@KVM03-10 ~]# qemu-img create /opt/test.raw 5G

#/opt/test.raw   虚拟磁盘存放的位置和文件名；

# 5G 虚拟磁盘大小；

[root@KVM03-10 ~]# qemu-img create /opt/test.raw
qemu-img: /opt/test.raw: Image creation needs a size parameter
[root@KVM03-10 ~]# qemu-img create /opt/test.raw 5G
Formatting '/opt/test.raw', fmt=raw size=5368709120
[root@KVM03-10 opt]#
[root@KVM03-10 opt]# ll -h
total 5.3G
-rw-------. 1 qemu qemu  10G Oct 11 10:32 centos2.1.raw
-rw-r--r--. 1 qemu qemu 4.1G Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root 5.0G Oct 11 10:37 test.raw
[root@KVM03-10 opt]#

[root@KVM03-10 opt]# qemu-img info test.raw
image: test.raw
file format: raw
virtual size: 5.0G (5368709120 bytes)
disk size: 0
[root@KVM03-10 opt]

其实以前Linux的dd命令同样可用于创建和负责磁盘并实现转换，具体可以man dd阅读或参照前辈的博客：https://www.cnblogs.com/ginvip/p/6370836.html

[root@KVM03-10 dev]# dd if=/dev/zero of=/opt/test-dd.raw bs=100M count=4
4+0 records in
4+0 records out
419430400 bytes (419 MB) copied, 1.93646 s, 217 MB/s
[root@KVM03-10 dev]# cd /opt/
[root@KVM03-10 opt]# ll -h
total 5.7G
-rw-------. 1 qemu qemu  10G Oct 11 10:46 centos2.1.raw
-rw-r--r--. 1 qemu qemu 4.1G Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root 400M Oct 11 10:58 test-dd.raw
-rw-r--r--. 1 root root 5.0G Oct 11 10:50 test.raw
[root@KVM03-10 opt]# qemu-img info test-dd.raw
image: test-dd.raw
file format: raw
virtual size: 400M (419430400 bytes)
disk size: 400M
[root@KVM03-10 opt]#

发现在不加磁盘类型参数的时候，默认创建的是raw类型磁盘，raw和qcow2格式各有优缺点，在创建的过程中可以指定磁盘格式，也可以创建完成后进行磁盘格式装换。下面就学习一下磁盘转换的命令。

create [-q] [-f fmt] [-o options] filename [size]   

'fmt' is the disk image format. It is guessed automatically in most cases

[root@KVM03-10 opt]# qemu-img  create -f qcow2 /opt/test.qcow2 2G
Formatting '/opt/test.qcow2', fmt=qcow2 size=2147483648 encryption=off cluster_size=65536 lazy_refcounts=off
[root@KVM03-10 opt]# ll
total 5520240
-rw-------. 1 qemu qemu 10737418240 Oct 11 11:21 centos2.1.raw
-rw-r--r--. 1 qemu qemu  4379901952 Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root  5368709120 Oct 11 11:19 test-1.raw
-rw-r--r--. 1 root root  5368709120 Oct 11 11:15 test-2.raw
-rw-r--r--. 1 root root      197120 Oct 11 11:24 test.qcow2
-rw-r--r--. 1 root root  5368709120 Oct 11 10:50 test.raw
[root@KVM03-10 opt]# qemu-img info test.qcow2
image: test.qcow2
file format: qcow2                          #文件类型：qcow2
virtual size: 2.0G (2147483648 bytes)　　　　　　#虚拟磁盘大小：2G
disk size: 196K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

3、磁盘格式转换

  convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-o options] [-s snapshot_name] [-S sparse_size] filename [filename2 [...]] output_filename

 # -f 原磁盘格式

# -O 目标磁盘格式

[root@KVM03-10 opt]# qemu-img convert -f raw -O qcow2 test.raw raw-to-qcow2.qcow2
[root@KVM03-10 opt]# ll
total 5509896
-rw-------. 1 qemu qemu 10737418240 Oct 11 11:51 centos2.1.raw
-rw-r--r--. 1 qemu qemu  4379901952 Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root      197120 Oct 11 11:55 raw-to-qcow2.qcow2
-rw-r--r--. 1 root root  1073741824 Oct 11 11:35 resize.raw
-rw-r--r--. 1 root root      262656 Oct 11 11:36 test.qcow2
-rw-r--r--. 1 root root  5368709120 Oct 11 10:50 test.raw
[root@KVM03-10 opt]#
[root@KVM03-10 opt]# qemu-img info raw-to-qcow2.qcow2
image: raw-to-qcow2.qcow2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
[root@KVM03-10 opt]#

 

 转换以后，不会对原文件有任何修改，而是新增一个文件目标磁盘格式的文件出来。这与电脑视频转换软件类似，转换以后原文件还在。

对文件进行转换后，修改虚机的xml文件中使用的磁盘文件，即可实现使用qcow2类型的磁盘文件启动。

  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/opt/centos2.1.raw.qcow2'/>           #修改虚机的磁盘文件
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>

[root@KVM03-10 ~]# virsh list --all
Id Name State
----------------------------------------------------
1 test-kvm running

好像不太对，虽然通过virsh list --all，可以看到正处于运行状态，但是通过vnc连接发现，启动异常。检查发现，还需要修改磁盘类型的参数！

  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/opt/centos2.1.raw.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </disk>

 

修改以后重新启用正常。

4、调整虚拟磁盘容量大小   resize [-q] filename [+ | -]size

创建完磁盘以后 ，可能需要对磁盘进行扩容操作，这个时候可以用过 qemu-img resize命令实现

 测试发现，qcow2和RAW格式的磁盘文件均支持扩容，但是仅raw格式文件支持缩容，qcow2不支持，这与两种磁盘文件类型有关，raw为连续的。另外，需要注意，在生产环境中，对磁盘进行缩容是危险操作，不建议缩容。

[root@KVM03-10 opt]# ll -h
total 5.3G
-rw-------. 1 qemu qemu  10G Oct 11 11:27 centos2.1.raw
-rw-r--r--. 1 qemu qemu 4.1G Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root 1.0G Oct 11 11:30 resize.raw
-rw-r--r--. 1 root root 193K Oct 11 11:24 test.qcow2
-rw-r--r--. 1 root root 5.0G Oct 11 10:50 test.raw
[root@KVM03-10 opt]# qemu-img resize resize.raw +1G
Image resized.
[root@KVM03-10 opt]# ll -h
total 5.3G
-rw-------. 1 qemu qemu  10G Oct 11 11:27 centos2.1.raw
-rw-r--r--. 1 qemu qemu 4.1G Apr 27 20:56 CentOS-7.3-x86_64-DVD-1611.iso
-rw-r--r--. 1 root root 2.0G Oct 11 11:31 resize.raw
-rw-r--r--. 1 root root 193K Oct 11 11:24 test.qcow2
-rw-r--r--. 1 root root 5.0G Oct 11 10:50 test.raw
[root@KVM03-10 opt]#