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kvm系列专题：磁盘扩容和添加磁盘

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kvm系列专题：磁盘扩容和添加磁盘

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在使用虚拟机时，如果磁盘空间沾满，我们该怎样扩容呢？
这篇文章分两种情况来讨论
情况一、虚拟机没有使用逻辑卷，直接扩容磁盘。
情况二、虚拟机使用了逻辑卷，添加一个磁盘，然后扩容逻辑卷。

先来聊聊情况一，虚拟机没有使用逻辑卷，怎样直接扩容磁盘以及虚拟机内的文件系统。
整体的大致步骤如下，先看一下，有个思路：
一、做好磁盘镜像备份
二、增加磁盘镜像的容量
三、登录虚拟机，扩容文件系统

此处以使用qcow2磁盘镜像的虚拟机为例，qcow2磁盘只支持增大，不支持缩小，所以我的模板机一般都设置的默认磁盘大小比较小，100G或者200G，而且都不是立即分配磁盘空间的，等真正用满的时候，再扩容也不迟，除非是一些确定需要大空间的应用，我会在虚拟机投入使用前就完成扩容，还有，生产环境中，一定要提前备份好磁盘镜像，避免操作失败后数据丢失。

备份完成后，确认需要扩容的磁盘没有快照，qcow2磁盘如果有快照，是不能扩容的，可使用virsh snapshot-list命令查看是否有虚拟机快照，或者使用qemu-img snapshot -l查看磁盘镜像是否有单独的磁盘快照，比如，查看kvm1的磁盘镜像的快照，可以使用如下命令

qemu-img snapshot -l /var/lib/libvirt/images/kvm1.qcow2
qemu-img snapshot -l /var/lib/libvirt/images/kvm1.qcow2
qemu-img snapshot -l /var/lib/libvirt/images/kvm1.qcow2

磁盘镜像如果有快照，无法进行扩容

再次确认，已经备份了需要扩容的磁盘，然后开始操作，此处以kvm4为例，从宿主机可以看到，目前kvm4已经启动

[root@cos7 ~]# virsh list --all
Id Name State
----------------------------------------------------
4 kvm4 running
- kvm1 shut off
- kvm2 shut off
- kvm3 shut off
- kvm5 shut off
- kvm6 shut off
[root@cos7 ~]# virsh list --all
 Id    Name                           State
----------------------------------------------------
 4     kvm4                           running
 -     kvm1                           shut off
 -     kvm2                           shut off
 -     kvm3                           shut off
 -     kvm5                           shut off
 -     kvm6                           shut off
[root@cos7 ~]# virsh list --all Id Name State ---------------------------------------------------- 4 kvm4 running - kvm1 shut off - kvm2 shut off - kvm3 shut off - kvm5 shut off - kvm6 shut off

登录kvm4，查看虚拟机磁盘状态，如下

[root@kvm4 ~]# fdisk -l
Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b9417
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 2099199 1048576 83 Linux
/dev/vda2 2099200 10227711 4064256 82 Linux swap / Solaris
/dev/vda3 10227712 104857599 47314944 83 Linux
[root@kvm4 ~]#
[root@kvm4 ~]#
[root@kvm4 ~]#
[root@kvm4 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 8.5M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/vda3 46G 1.3G 44G 3% /
/dev/vda1 1014M 142M 873M 14% /boot
tmpfs 379M 0 379M 0% /run/user/0
[root@kvm4 ~]# fdisk -l

Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b9417

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     2099199     1048576   83  Linux
/dev/vda2         2099200    10227711     4064256   82  Linux swap / Solaris
/dev/vda3        10227712   104857599    47314944   83  Linux
[root@kvm4 ~]# 
[root@kvm4 ~]# 
[root@kvm4 ~]# 
[root@kvm4 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        1.9G     0  1.9G   0% /dev
tmpfs           1.9G     0  1.9G   0% /dev/shm
tmpfs           1.9G  8.5M  1.9G   1% /run
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/vda3        46G  1.3G   44G   3% /
/dev/vda1      1014M  142M  873M  14% /boot
tmpfs           379M     0  379M   0% /run/user/0
[root@kvm4 ~]# fdisk -l Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000b9417 Device Boot Start End Blocks Id System /dev/vda1 * 2048 2099199 1048576 83 Linux /dev/vda2 2099200 10227711 4064256 82 Linux swap / Solaris /dev/vda3 10227712 104857599 47314944 83 Linux [root@kvm4 ~]# [root@kvm4 ~]# [root@kvm4 ~]# [root@kvm4 ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 1.9G 0 1.9G 0% /dev tmpfs 1.9G 0 1.9G 0% /dev/shm tmpfs 1.9G 8.5M 1.9G 1% /run tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup /dev/vda3 46G 1.3G 44G 3% / /dev/vda1 1014M 142M 873M 14% /boot tmpfs 379M 0 379M 0% /run/user/0

从上述信息可以看出，目前kvm4虚拟机只有一块vda磁盘，有三个分区，/dev/vda1分区是boot分区，/dev/vda2是swap分区，/dev/vda3是根文件系统，根的大小是46G，44G可用，此处假设，根分区已经沾满了，我们需要扩容根分区，虽然最终目标是扩容根分区，但是需要先在宿主机上，为kvm4的磁盘进行扩容，扩容完磁盘后，再扩容分区的文件系统。
在宿主机上确认kvm4的磁盘镜像路径，如下：

[root@cos7 ~]# virsh domblklist kvm4
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/kvm4.qcow2
[root@cos7 ~]# virsh domblklist kvm4
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/kvm4.qcow2
hda        -
[root@cos7 ~]# virsh domblklist kvm4 Target Source ------------------------------------------------ vda /var/lib/libvirt/images/kvm4.qcow2 hda -

可以看到，kvm4的磁盘镜像路径是/var/lib/libvirt/images/kvm4.qcow2，对应挂载到了kvm4的vda磁盘，先看一下目前磁盘镜像的大小

[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2
image: /var/lib/libvirt/images/kvm4.qcow2
file format: qcow2
virtual size: 50G (53687091200 bytes)
disk size: 1.5G
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: true
[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2
image: /var/lib/libvirt/images/kvm4.qcow2
file format: qcow2
virtual size: 50G (53687091200 bytes)
disk size: 1.5G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2 image: /var/lib/libvirt/images/kvm4.qcow2 file format: qcow2 virtual size: 50G (53687091200 bytes) disk size: 1.5G cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: true

如上所示，磁盘虚拟大小为50G，目前占用宿主机1.5G空间，磁盘格式是一个qcow2的磁盘。
现在，我们要扩容这个磁盘镜像，增容20G的空间，但是在操作之前，请先停止虚拟机，虽然不停止也可以增容成功，但是会报错，目前还不清楚，错误是否会对虚拟机以后的运行产生影响，保险起见，先停止虚拟机，然后再执行如下命令对磁盘镜像进行扩容。
停止虚拟机后，执行如下命令

[root@cos7 ~]# qemu-img resize /var/lib/libvirt/images/kvm4.qcow2 +20G
Image resized.
[root@cos7 ~]# qemu-img resize /var/lib/libvirt/images/kvm4.qcow2 +20G
Image resized.
[root@cos7 ~]# qemu-img resize /var/lib/libvirt/images/kvm4.qcow2 +20G Image resized.

增容后，再次查看磁盘镜像信息，如下，磁盘的virtual size已经从50G变成了70G

[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2
image: /var/lib/libvirt/images/kvm4.qcow2
file format: qcow2
virtual size: 70G (75161927680 bytes)
disk size: 2.5G
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: true
[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2
image: /var/lib/libvirt/images/kvm4.qcow2
file format: qcow2
virtual size: 70G (75161927680 bytes)
disk size: 2.5G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
[root@cos7 ~]# qemu-img info /var/lib/libvirt/images/kvm4.qcow2 image: /var/lib/libvirt/images/kvm4.qcow2 file format: qcow2 virtual size: 70G (75161927680 bytes) disk size: 2.5G cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: true

磁盘扩容成功后，启动kvm4虚拟机，登录到虚拟机内，再次查看磁盘信息，发现已经变成了75G

[root@kvm4 ~]# fdisk -l
Disk /dev/vda: 75.2 GB, 75161927680 bytes, 146800640 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b9417
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 2099199 1048576 83 Linux
/dev/vda2 2099200 10227711 4064256 82 Linux swap / Solaris
/dev/vda3 10227712 104857599 47314944 83 Linux
[root@kvm4 ~]# fdisk -l

Disk /dev/vda: 75.2 GB, 75161927680 bytes, 146800640 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b9417

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     2099199     1048576   83  Linux
/dev/vda2         2099200    10227711     4064256   82  Linux swap / Solaris
/dev/vda3        10227712   104857599    47314944   83  Linux
[root@kvm4 ~]# fdisk -l Disk /dev/vda: 75.2 GB, 75161927680 bytes, 146800640 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000b9417 Device Boot Start End Blocks Id System /dev/vda1 * 2048 2099199 1048576 83 Linux /dev/vda2 2099200 10227711 4064256 82 Linux swap / Solaris /dev/vda3 10227712 104857599 47314944 83 Linux

但是，根分区和对应的文件系统还没有扩容，如下，可以看到/dev/vda3分区仍然识别为48G，根文件系统仍然识别为46G。

[root@kvm4 ~]# fdisk -lu /dev/vda3
Disk /dev/vda3: 48.5 GB, 48450502656 bytes, 94629888 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm4 ~]#
[root@kvm4 ~]#
[root@kvm4 ~]#
[root@kvm4 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 8.5M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/vda3 46G 1.3G 44G 3% /
/dev/vda1 1014M 142M 873M 14% /boot
tmpfs 379M 0 379M 0% /run/user/0
[root@kvm4 ~]# fdisk -lu /dev/vda3

Disk /dev/vda3: 48.5 GB, 48450502656 bytes, 94629888 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

[root@kvm4 ~]# 
[root@kvm4 ~]# 
[root@kvm4 ~]# 
[root@kvm4 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        1.9G     0  1.9G   0% /dev
tmpfs           1.9G     0  1.9G   0% /dev/shm
tmpfs           1.9G  8.5M  1.9G   1% /run
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/vda3        46G  1.3G   44G   3% /
/dev/vda1      1014M  142M  873M  14% /boot
tmpfs           379M     0  379M   0% /run/user/0
[root@kvm4 ~]# fdisk -lu /dev/vda3 Disk /dev/vda3: 48.5 GB, 48450502656 bytes, 94629888 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes [root@kvm4 ~]# [root@kvm4 ~]# [root@kvm4 ~]# [root@kvm4 ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 1.9G 0 1.9G 0% /dev tmpfs 1.9G 0 1.9G 0% /dev/shm tmpfs 1.9G 8.5M 1.9G 1% /run tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup /dev/vda3 46G 1.3G 44G 3% / /dev/vda1 1014M 142M 873M 14% /boot tmpfs 379M 0 379M 0% /run/user/0

我们现在的目标就是扩容根分区和文件系统。
此处可以参考阿里云的文档进行扩容操作，链接如下：
https://help.aliyun.com/document_detail/113316.html?spm=5176.21213303.J_6028563670.36.241a3edapvGQJG&scm=20140722.S_help

我的虚拟机操作系统是centos7，分区是MBR分区，不是GPT分区，文件系统是xfs，所以，我的扩容过程可能跟实际遇到的情况不太一样，这里需要以实际情况为准，参考上面的文档，做出不同的细节处理，生产环境中最好提前克隆出一个机器或者做一个测试机进行模拟。

首先，在虚拟机中安装cloud-utils-growpart工具（如果是GPT分区，先安装gdisk），对分区进行扩容，centos7中命令如下

yum install -y cloud-utils-growpart
yum install -y cloud-utils-growpart
yum install -y cloud-utils-growpart

安装完成后，执行如下命令扩容对应分区，我需要扩容vda3，所以命令中是vda 3，vda和3中间有空格

[root@kvm4 ~]# growpart /dev/vda 3
CHANGED: partition=3 start=10227712 old: size=94629888 end=104857600 new: size=136572895 end=146800607
[root@kvm4 ~]# growpart /dev/vda 3
CHANGED: partition=3 start=10227712 old: size=94629888 end=104857600 new: size=136572895 end=146800607
[root@kvm4 ~]# growpart /dev/vda 3 CHANGED: partition=3 start=10227712 old: size=94629888 end=104857600 new: size=136572895 end=146800607

可以看到，分区的大小已经改变，使用命令确认，vda3分区的大小已经识别为69.9G

[root@kvm4 ~]# fdisk -lu /dev/vda3
Disk /dev/vda3: 69.9 GB, 69925322240 bytes, 136572895 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm4 ~]# fdisk -lu /dev/vda3

Disk /dev/vda3: 69.9 GB, 69925322240 bytes, 136572895 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm4 ~]# fdisk -lu /dev/vda3 Disk /dev/vda3: 69.9 GB, 69925322240 bytes, 136572895 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes

如果扩容完成后，再次执行扩容命令，会提示NOCHANGE…it cannot be grown，这是因为，分区已经扩展完成了，没有富裕的空间可供扩展了，其实，还有一种情况也会报如下错误，导致无法扩容分区，我们一会儿再聊，先把一整套扩容流程走完，此处重复执行如下命令不会影响扩容。

[root@kvm4 ~]# growpart /dev/vda 3
NOCHANGE: partition 3 is size 136572895. it cannot be grown
[root@kvm4 ~]# growpart /dev/vda 3
NOCHANGE: partition 3 is size 136572895. it cannot be grown
[root@kvm4 ~]# growpart /dev/vda 3 NOCHANGE: partition 3 is size 136572895. it cannot be grown

vda3分区扩容完成后，需要扩容分区对应的文件系统，此处文件系统是xfs，所以执行xfs_growfs命令即可，如果是ext文件系统，需要使用resize2fs命令，此处运行的命令为xfs_growfs /dev/vda3
如下：

[root@kvm4 ~]# xfs_growfs /dev/vda3
meta-data=/dev/vda3 isize=512 agcount=4, agsize=2957184 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0 spinodes=0
data = bsize=4096 blocks=11828736, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=5775, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 11828736 to 17071611
[root@kvm4 ~]# xfs_growfs /dev/vda3
meta-data=/dev/vda3              isize=512    agcount=4, agsize=2957184 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=11828736, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal               bsize=4096   blocks=5775, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 11828736 to 17071611
[root@kvm4 ~]# xfs_growfs /dev/vda3 meta-data=/dev/vda3 isize=512 agcount=4, agsize=2957184 blks = sectsz=512 attr=2, projid32bit=1 = crc=1 finobt=0 spinodes=0 data = bsize=4096 blocks=11828736, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 ftype=1 log =internal bsize=4096 blocks=5775, version=2 = sectsz=512 sunit=0 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 data blocks changed from 11828736 to 17071611

再次查看磁盘使用情况，可以看到，根分区已经从之前的46G扩容到了66G，如下

[root@kvm4 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 8.5M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/vda3 66G 1.4G 64G 3% /
/dev/vda1 1014M 142M 873M 14% /boot
tmpfs 379M 0 379M 0% /run/user/0
[root@kvm4 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        1.9G     0  1.9G   0% /dev
tmpfs           1.9G     0  1.9G   0% /dev/shm
tmpfs           1.9G  8.5M  1.9G   1% /run
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/vda3        66G  1.4G   64G   3% /
/dev/vda1      1014M  142M  873M  14% /boot
tmpfs           379M     0  379M   0% /run/user/0
[root@kvm4 ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 1.9G 0 1.9G 0% /dev tmpfs 1.9G 0 1.9G 0% /dev/shm tmpfs 1.9G 8.5M 1.9G 1% /run tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup /dev/vda3 66G 1.4G 64G 3% / /dev/vda1 1014M 142M 873M 14% /boot tmpfs 379M 0 379M 0% /run/user/0

至此，整个扩容操作已经完成了。

此处有一个坑，刚才已经提到过，在扩容分区时，我们使用了growpart命令，如果重复执行此命令，会提示NOCHANGE…it cannot be grown，这是因为已经没有更多空间可供分区扩容了，但是，在某些特殊情况下，磁盘明明还有很多空间，在第一次执行growpart命令时就会提示it cannot be grown，现在咱们就来聊聊这种特殊情况。

如果磁盘有很多富裕空间可供分区扩容，但是每次执行growpart命令就提示it cannot be grown，很有可能是因为，你要扩容的分区不是磁盘的最后一个分区，上例中，我要扩容的vda3就是vda磁盘的最后一个分区，如下图，可以通过分区号或者分区区间很明显的看出，vda3就是vda的最后一个分区
16363641495252.jpg
这种情况下，第一次执行growpart命令扩容分区时，应该是可以正常执行的。
但是，如果你遇到的分区是下面的情况，而你想要扩容的分区恰巧不是磁盘的最后一个分区，则无法扩容成功，会直接提示it cannot be grown

[root@kvm1 ~]# fdisk -l
Disk /dev/vda: 536.9 GB, 536870912000 bytes, 1048576000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ac5a2
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 2099199 1048576 83 Linux
/dev/vda2 2099200 1044367359 521134080 83 Linux
/dev/vda3 1044367360 1048561663 2097152 82 Linux swap / Solaris
[root@kvm1 ~]#
[root@kvm1 ~]#
[root@kvm1 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 909M 0 909M 0% /dev
tmpfs 919M 0 919M 0% /dev/shm
tmpfs 919M 8.6M 911M 1% /run
tmpfs 919M 0 919M 0% /sys/fs/cgroup
/dev/vda2 497G 1.3G 496G 1% /
/dev/vda1 1014M 142M 873M 14% /boot
tmpfs 184M 0 184M 0% /run/user/0
[root@kvm1 ~]# fdisk -l

Disk /dev/vda: 536.9 GB, 536870912000 bytes, 1048576000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ac5a2

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     2099199     1048576   83  Linux
/dev/vda2         2099200  1044367359   521134080   83  Linux
/dev/vda3      1044367360  1048561663     2097152   82  Linux swap / Solaris
[root@kvm1 ~]# 
[root@kvm1 ~]# 
[root@kvm1 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        909M     0  909M   0% /dev
tmpfs           919M     0  919M   0% /dev/shm
tmpfs           919M  8.6M  911M   1% /run
tmpfs           919M     0  919M   0% /sys/fs/cgroup
/dev/vda2       497G  1.3G  496G   1% /
/dev/vda1      1014M  142M  873M  14% /boot
tmpfs           184M     0  184M   0% /run/user/0
[root@kvm1 ~]# fdisk -l Disk /dev/vda: 536.9 GB, 536870912000 bytes, 1048576000 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000ac5a2 Device Boot Start End Blocks Id System /dev/vda1 * 2048 2099199 1048576 83 Linux /dev/vda2 2099200 1044367359 521134080 83 Linux /dev/vda3 1044367360 1048561663 2097152 82 Linux swap / Solaris [root@kvm1 ~]# [root@kvm1 ~]# [root@kvm1 ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 909M 0 909M 0% /dev tmpfs 919M 0 919M 0% /dev/shm tmpfs 919M 8.6M 911M 1% /run tmpfs 919M 0 919M 0% /sys/fs/cgroup /dev/vda2 497G 1.3G 496G 1% / /dev/vda1 1014M 142M 873M 14% /boot tmpfs 184M 0 184M 0% /run/user/0

如上，vda一共有三个分区，根对应的分区是vda2，即使vda磁盘有很多富裕空间，如果想要使用growpart命令扩容vda2，也是不行的，会直接提示it cannot be grown，因为上例中，vda2后面还有一个vda3分区，而上例中的情况比较好处理，因为最后一个分区是swap分区，我们只需要删除这个分区，然后再扩容vda2就好了，扩容完成后，再单独挂载一个磁盘作为swap分区或者使用文件作为swap分区，所以，在做模板机的时候要避开这个坑，别问我怎么知道的。

直接扩容磁盘和文件系统的情况已经描述清楚了，现在说说添加一个磁盘，扩展lvm逻辑卷的情况，其实这里描述的重点是怎样为虚拟机添加一块磁盘，磁盘添加后，是用来扩展逻辑卷，还是单独作为一个分区使用，就看具体情况了，所以此处只演示为虚拟机添加磁盘和卸载磁盘的操作，此处以kvm6为例进行演示，kvm6已经启动了，查看kvm6当前的磁盘有哪些，在宿主机执行如下命令：

[root@cos7 ~]# virsh domblklist kvm6
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/kvm6.qcow2
vdb /var/lib/libvirt/images/kvm6_vdb.qcow2
[root@cos7 ~]# virsh domblklist kvm6
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/kvm6.qcow2
vdb        /var/lib/libvirt/images/kvm6_vdb.qcow2
hda        -
[root@cos7 ~]# virsh domblklist kvm6 Target Source ------------------------------------------------ vda /var/lib/libvirt/images/kvm6.qcow2 vdb /var/lib/libvirt/images/kvm6_vdb.qcow2 hda -

可以看到，kvm6已经有两块磁盘了，分别对应vda和vdb，现在，创建一块新的磁盘，我准备将新创建的磁盘对应到kvm6的vdc上，所以直接为磁盘文件命名为kvm6_vdc.qcow2，注意！在同路径下，不要与现有的盘重名，否则会清空同名盘，命令如下：

qemu-img create -f qcow2 /var/lib/libvirt/images/kvm6_vdc.qcow2 5G
qemu-img create -f qcow2 /var/lib/libvirt/images/kvm6_vdc.qcow2 5G
qemu-img create -f qcow2 /var/lib/libvirt/images/kvm6_vdc.qcow2 5G

我们已经创建好了磁盘，但是还没有将磁盘添加到kvm6上，在添加磁盘之前，先看看kvm6的配置文件，磁盘部分的配置如下，其他配置省略了

<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/kvm6.qcow2'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/>
<target dev='vdb' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/kvm6.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
<disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/kvm6.qcow2'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/> <target dev='vdb' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/> </disk>

从配置文件中可以再次印证，目前有kvm6有两块盘，当我们将次三块盘添加到kvm6以后，会多出一段第三块盘的配置。

确保kvm6开机后，使用如下命令，将磁盘添加到kvm6虚拟机上，如下添加磁盘的操作，只能在虚拟机开机的情况下执行。

virsh attach-disk --domain kvm6 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vdc --targetbus virtio --persistent
virsh attach-disk --domain kvm6 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vdc --targetbus virtio --persistent
virsh attach-disk --domain kvm6 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vdc --targetbus virtio --persistent

如上所示，使用virsh attach-disk为指定的虚拟机添加磁盘，–domain指定虚拟机名，–source指定要添加的磁盘文件，–subdriver指定磁盘文件的格式，由于我使用的是qcow2格式的磁盘，所以此处不能省略–subdriver参数，如果省略此参数，默认会被当做raw格式的磁盘，如果被当做raw格式的磁盘，磁盘挂载后，对应的磁盘空间会识别为磁盘实际占用的大小（与宿主机中识别的大小一样，测试的qcow2没有预分配空间），所以此处使用–subdriver qcow2指明磁盘格式，–target参数用来指定磁盘文件对应虚拟机中的哪个磁盘，这里有个坑，如果这个磁盘是第一次被使用，那么使用target指定的目标是通常准确的，如果这块盘其他虚拟机使用过，那么target指定后的目标可能会出现误差（有一定几率），这样描述可能让你无法理解是什么意思，此处先不聊这个小坑，文章最后再做详细的解释。–targetbus virtio用来指定是否使用virtio总线驱动，由于我的虚拟机是centos7，默认支持virtio，所以添加上了，具体还需要根据虚拟机操作系统的实际情况，决定是否添加，–persistent参数表示配置是否永久生效，如果不添加–persistent参数，磁盘只是临时添加到虚拟机中，虚拟机断电重启后，不会再有对应的新磁盘，也就是说，不加–persistent参数，虚拟机的xml配置文件是不会被修改的，如果加上–persistent参数，虚拟机的xml配置文件会被自动修改，添加上新磁盘的配置。

执行上述命令后，再次查看kvm6的xml配置文件，会发现多出了新磁盘的配置，如下

<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/kvm6.qcow2'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/>
<target dev='vdb' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source file='/var/lib/libvirt/images/kvm6_vdc.qcow2'/>
<target dev='vdc' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/kvm6.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/kvm6_vdc.qcow2'/>
      <target dev='vdc' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
    </disk>
<disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/kvm6.qcow2'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/kvm6_vdb.qcow2'/> <target dev='vdb' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/> </disk> <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/kvm6_vdc.qcow2'/> <target dev='vdc' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/> </disk>

如上所示，最后一块盘的配置就是我们添加的新盘，因为我们在添加磁盘时，使用了–persistent参数，进入虚拟机，查看磁盘列表，已经可以看到新加入的磁盘了。

[root@kvm6 ~]# fdisk -l
Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ba397
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 2099199 1048576 83 Linux
/dev/vda2 2099200 104857599 51379200 8e Linux LVM
Disk /dev/vdb: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/centos-root: 53.8 GB, 53812920320 bytes, 105103360 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm6 ~]# fdisk -l

Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ba397

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     2099199     1048576   83  Linux
/dev/vda2         2099200   104857599    51379200   8e  Linux LVM

Disk /dev/vdb: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/centos-root: 53.8 GB, 53812920320 bytes, 105103360 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm6 ~]# fdisk -l Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000ba397 Device Boot Start End Blocks Id System /dev/vda1 * 2048 2099199 1048576 83 Linux /dev/vda2 2099200 104857599 51379200 8e Linux LVM Disk /dev/vdb: 10.7 GB, 10737418240 bytes, 20971520 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/centos-root: 53.8 GB, 53812920320 bytes, 105103360 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes

现在要做的就是初始化磁盘了，根据需求不同，做出不同的操作，比如，是创建pv加入到卷组中，还是作为一个单独的分区使用，就看具体情况了，为了方便演示，此处直接当做一个挂载点去使用，需要注意的是，在设置完成后，配置好自动挂载，此处不分区，直接为vdc创建xfs文件系统。

[root@kvm6 ~]# mkfs.xfs /dev/vdc
meta-data=/dev/vdc isize=512 agcount=4, agsize=327680 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0, sparse=0
data = bsize=4096 blocks=1310720, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
[root@kvm6 ~]# mkfs.xfs /dev/vdc
meta-data=/dev/vdc               isize=512    agcount=4, agsize=327680 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=1310720, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@kvm6 ~]# mkfs.xfs /dev/vdc meta-data=/dev/vdc isize=512 agcount=4, agsize=327680 blks = sectsz=512 attr=2, projid32bit=1 = crc=1 finobt=0, sparse=0 data = bsize=4096 blocks=1310720, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 ftype=1 log =internal log bsize=4096 blocks=2560, version=2 = sectsz=512 sunit=0 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0

创建一个测试目录当做挂载点，挂载新的硬盘

[root@kvm6 ~]# mkdir /testdisk
[root@kvm6 ~]# mount /dev/vdc /testdisk
[ 1010.692185] XFS (vdc): Mounting V5 Filesystem
[ 1010.711786] XFS (vdc): Ending clean mount
[root@kvm6 ~]#
[root@kvm6 ~]#
[root@kvm6 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs 1.9G 0 1.9G 0% /dev/shm
tmpfs 1.9G 8.5M 1.9G 1% /run
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/mapper/centos-root 51G 1.3G 49G 3% /
/dev/vda1 1014M 150M 865M 15% /boot
tmpfs 379M 0 379M 0% /run/user/0
/dev/vdc 5.0G 33M 5.0G 1% /testdisk
[root@kvm6 ~]# mkdir /testdisk
[root@kvm6 ~]# mount /dev/vdc /testdisk
[ 1010.692185] XFS (vdc): Mounting V5 Filesystem
[ 1010.711786] XFS (vdc): Ending clean mount
[root@kvm6 ~]# 
[root@kvm6 ~]# 
[root@kvm6 ~]# df -h
Filesystem               Size  Used Avail Use% Mounted on
devtmpfs                 1.9G     0  1.9G   0% /dev
tmpfs                    1.9G     0  1.9G   0% /dev/shm
tmpfs                    1.9G  8.5M  1.9G   1% /run
tmpfs                    1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/mapper/centos-root   51G  1.3G   49G   3% /
/dev/vda1               1014M  150M  865M  15% /boot
tmpfs                    379M     0  379M   0% /run/user/0
/dev/vdc                 5.0G   33M  5.0G   1% /testdisk
[root@kvm6 ~]# mkdir /testdisk [root@kvm6 ~]# mount /dev/vdc /testdisk [ 1010.692185] XFS (vdc): Mounting V5 Filesystem [ 1010.711786] XFS (vdc): Ending clean mount [root@kvm6 ~]# [root@kvm6 ~]# [root@kvm6 ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 1.9G 0 1.9G 0% /dev tmpfs 1.9G 0 1.9G 0% /dev/shm tmpfs 1.9G 8.5M 1.9G 1% /run tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup /dev/mapper/centos-root 51G 1.3G 49G 3% / /dev/vda1 1014M 150M 865M 15% /boot tmpfs 379M 0 379M 0% /run/user/0 /dev/vdc 5.0G 33M 5.0G 1% /testdisk

实际使用中，记得修改fstab，把磁盘自动挂载（当然如果是逻辑卷就另说），而且需要注意，设置自动挂载时，应该用磁盘的UUID，使用UUID是最准确最保险的。

磁盘挂载已经完成了，现在来看看怎样卸载磁盘，操作如下
如果之前设置过自动挂载，先把对应的自动挂载配置注释了，避免卸载磁盘后，找不到对应的磁盘影响启动。
确定取消自动挂载后，在虚拟机系统内卸载对应的挂载点，卸载挂载点后，确保虚拟机正在运行，在宿主机中执行如下命令，

virsh detach-disk kvm6 /var/lib/libvirt/images/kvm6_vdc.qcow2 --persistent
virsh detach-disk kvm6 /var/lib/libvirt/images/kvm6_vdc.qcow2 --persistent
virsh detach-disk kvm6 /var/lib/libvirt/images/kvm6_vdc.qcow2 --persistent

执行上述命令后，磁盘卸载操作直接生效，并且永久生效，与添加磁盘同理，–persistent参数会修改配置文件，将对应的磁盘配置段删除。

卸载下来的磁盘也可以挂载到其他虚拟机上使用，比如，我刚刚从kvm6上卸载了kvm6_vdc.qcow2这块磁盘，现在我想把这块磁盘挂载到kvm5上使用，也是可以的，但是可能会遇到一些小问题，我们先来查看一下kvm5目前都有哪些磁盘

[root@cos7 ~]# virsh domblklist kvm5
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/kvm5.qcow2
[root@cos7 ~]# virsh domblklist kvm5
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/kvm5.qcow2
hda        -
[root@cos7 ~]# virsh domblklist kvm5 Target Source ------------------------------------------------ vda /var/lib/libvirt/images/kvm5.qcow2 hda -

如上所示，只有一块磁盘，对应虚拟机中的vda，此时，我们执行如下命令，将kvm6卸载下的盘挂载到kvm5上，临时挂载命令如下：

[root@cos7 ~]# virsh attach-disk --domain kvm5 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vde --targetbus virtio
Disk attached successfully
[root@cos7 ~]# virsh domblklist kvm5
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/kvm5.qcow2
vde /var/lib/libvirt/images/kvm6_vdc.qcow2
[root@cos7 ~]# virsh attach-disk --domain kvm5 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vde --targetbus virtio
Disk attached successfully

[root@cos7 ~]# virsh domblklist kvm5
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/kvm5.qcow2
vde        /var/lib/libvirt/images/kvm6_vdc.qcow2
hda        -
[root@cos7 ~]# virsh attach-disk --domain kvm5 --source /var/lib/libvirt/images/kvm6_vdc.qcow2 --subdriver qcow2 --target vde --targetbus virtio Disk attached successfully [root@cos7 ~]# virsh domblklist kvm5 Target Source ------------------------------------------------ vda /var/lib/libvirt/images/kvm5.qcow2 vde /var/lib/libvirt/images/kvm6_vdc.qcow2 hda -

如上所示，我们将kvm6_vdc.qcow2挂载到了kvm5上，并且指定kvm6_vdc.qcow2对应kvm5的vde，从宿主机上查看，kvm6_vdc.qcow2的确对应的是vde，但是进入kvm5，会发现，新加入的盘符并不是vde，而是vdc，如下所示

[root@kvm5 /]# fdisk -l
Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ba397
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 2099199 1048576 83 Linux
/dev/vda2 2099200 104857599 51379200 8e Linux LVM
Disk /dev/mapper/centos-root: 48.4 GB, 48444211200 bytes, 94617600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm5 /]# fdisk -l

Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ba397

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     2099199     1048576   83  Linux
/dev/vda2         2099200   104857599    51379200   8e  Linux LVM

Disk /dev/mapper/centos-root: 48.4 GB, 48444211200 bytes, 94617600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
[root@kvm5 /]# fdisk -l Disk /dev/vda: 53.7 GB, 53687091200 bytes, 104857600 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x000ba397 Device Boot Start End Blocks Id System /dev/vda1 * 2048 2099199 1048576 83 Linux /dev/vda2 2099200 104857599 51379200 8e Linux LVM Disk /dev/mapper/centos-root: 48.4 GB, 48444211200 bytes, 94617600 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/mapper/centos-swap: 4160 MB, 4160749568 bytes, 8126464 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk /dev/vdc: 5368 MB, 5368709120 bytes, 10485760 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes

之前实验过，有时会被识别成顺位最新的一个盘符，比如，虚拟机只有一块vda，在宿主机中指定的target是vdc，但是自动识别成第二个盘符vdb的，不过有时也会准确的按照target指定的盘符去识别，通过实验无法确定原因，所以这是一个注意点，我们只需要记住，如果磁盘是使用过的，当添加到虚拟机时，使用–target指定盘符后，在虚拟机中实际识别的结果可能是有误差的，有可能与在宿主机中查看的结果不一致，需要以实际情况为准，最好按照盘符的顺位指定target，中间不要隔着没有使用的盘符，比如vda后应该是vdb，那么就指定用vdb，而不是直接跳过vdb，指定vdc或者vdd，这样容易出问题，如果出现误差，可以尝试卸载后再次挂载。


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