kvm虚拟机也支持在线扩展磁盘功能,在线扩展有特定的使用环境，主要用于不能随便停用的生产环境中，本文以hadoop为例具体步骤如下：

1，查看现有磁盘

[root@KVM test]# virsh list --all
 Id    Name                           State
----------------------------------------------------
 1     win7                           running
 17    hadoop1                        running
 18    hadoop4                        running
 20    hadoop2                        running
 -     hadoop3                        shut off
[root@KVM test]# virsh domblklist hadoop1
Target     Source
------------------------------------------------
vda        /p_w_picpaths/test/hadoop1.qcow2
hdc        -

2，创建一块qcow2虚拟磁盘

[root@KVM test]# qemu-img create -f qcow2 hadoop1_add01.qcow2 5G
Formatting 'hadoop1_add01.qcow2', fmt=qcow2 size=5368709120 encryption=off cluster_size=65536 
[root@KVM test]#

3，在线添加这台qcow2虚拟磁盘

[root@KVM test]# virsh attach-disk hadoop1 /p_w_picpaths/test/hadoop1_add01.qcow2 vdb --cache=none --subdriver=qcow2            
Disk attached successfully
[root@KVM test]# virsh domblklist hadoop1                       
Target     Source
------------------------------------------------
vda        /p_w_picpaths/test/hadoop1.qcow2
vdb        /p_w_picpaths/test/hadoop1_add01.qcow2
hdc        -

6,划分逻辑卷LVM省略，前边的可以参考。

7，修改虚拟机配置文件，把新增的磁盘配置写到虚拟机磁盘配置

 （1）查看当前虚拟机hadoop1的磁盘配置

[root@KVM test]# virsh dumpxml hadoop1
<domain type='qemu' id='17'>
  <name>hadoop1</name>
  <uuid>919f0921-0736-ad5b-780b-a440de2f35cb</uuid>
  <memory unit='KiB'>524288</memory>
  <currentMemory unit='KiB'>524288</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <os>
    <type arch='x86_64' machine='rhel6.6.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/p_w_picpaths/test/hadoop1.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/p_w_picpaths/test/hadoop1_add01.qcow2'/>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
    <disk type='block' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <alias name='ide0-1-0'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <alias name='usb0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <alias name='usb0'/>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <alias name='usb0'/>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <alias name='usb0'/>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x2'/>
    </controller>
    <controller type='ide' index='0'>
      <alias name='ide0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:b6:bf:1f'/>
      <source bridge='br0'/>
      <target dev='vnet1'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/2'/>
      <target port='0'/>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/2'>
      <source path='/dev/pts/2'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5911' autoport='no' listen='0.0.0.0'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </memballoon>
  </devices>
</domain>

 （2）把以下配置添加到/etc/libvirt/qemu/hadoop1.xml配置文件中

 <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/p_w_picpaths/test/hadoop1_add01.qcow2'/>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>

当把所有的配置文件写到虚拟机的配置信息后，及时重启也能生效。