Virtualization With KVM On A Fedora 17 Server - Page 5

8 Creating An LVM-Based Guest From The Command Line

Fedora 17 KVM Host:

LVM-based guests have some advantages over image-based guests. They are not as heavy on hard disk IO, and they are easier to back up (using LVM snapshots).

To use LVM-based guests, you need a volume group that has some free space that is not allocated to any logical volume. In this example, I use the volume group /dev/vg_server1 with a size of approx. 465GB...


[root@server1 ~]# vgdisplay
  --- Volume group ---
  VG Name               vg_server1
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               465.28 GiB
  PE Size               4.00 MiB
  Total PE              119112
  Alloc PE / Size       26500 / 103.52 GiB
  Free  PE / Size       92612 / 361.77 GiB
  VG UUID               ZXWn5k-oVkA-ibuC-ip8x-edLx-3DMw-UrYMXg

[root@server1 ~]#

... that contains the logical volumes /dev/vg_server1/LogVol00 with a size of approx. 100GB and /dev/vg_server1/LogVol01 (about 6GB) - the rest is not allocated and can be used for KVM guests:


[root@server1 ~]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/vg_server1/LogVol01
  LV Name                LogVol01
  VG Name                vg_server1
  LV UUID                uUpXY3-yGfZ-X6bc-3D1u-gB4E-CfKE-vDcNfw
  LV Write Access        read/write
  LV Creation host, time, 2012-08-21 13:45:32 +0200
  LV Status              available
  # open                 1
  LV Size                5.86 GiB
  Current LE             1500
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

  --- Logical volume ---
  LV Path                /dev/vg_server1/LogVol00
  LV Name                LogVol00
  VG Name                vg_server1
  LV UUID                FN1404-Aczo-9dfA-CnNI-IKn0-L2hW-Aix0rV
  LV Write Access        read/write
  LV Creation host, time, 2012-08-21 13:45:33 +0200
  LV Status              available
  # open                 1
  LV Size                97.66 GiB
  Current LE             25000
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

[root@server1 ~]#

I will now create the virtual machine vm12 as an LVM-based guest. I want vm12 to have 20GB of disk space, so I create the logical volume /dev/vg_server1/vm12 with a size of 20GB:

lvcreate -L20G -n vm12 vg_server1

Afterwards, we use the virt-install command again to create the guest:

virt-install --connect qemu:///system -n vm12 -r 512 --vcpus=2 --disk path=/dev/vg_server1/vm12 -c /var/lib/libvirt/images/debian-6.0.5-amd64-netinst.iso --vnc --noautoconsole --os-type linux --os-variant debiansqueeze --accelerate --network=bridge:br0 --hvm

Please note that instead of --disk path=/var/lib/libvirt/images/vm12.img,size=20 I use --disk path=/dev/vg_server1/vm12, and I don't need to define the disk space anymore because the disk space is defined by the size of the logical volume vm12 (20GB).

Now follow chapter 5 to install that guest.


9 Converting Image-Based Guests To LVM-Based Guests

Fedora 17 KVM Host:

No let's assume we want to convert our image-based guest vm10 into an LVM-based guest. This is how we do it:

First make sure the guest is stopped:

virsh --connect qemu:///system

shutdown vm10


Then create a logical volume (e.g. /dev/vg_server1/vm10) that has the same size as the image file. To find out the size of the image, type in ...

ls -l /var/lib/libvirt/images/

[root@server1 ~]# ls -l /var/lib/libvirt/images/
total 13819392
-rw-r--r-- 1 qemu qemu   177209344 May 12 22:41 debian-6.0.5-amd64-netinst.iso
-rw------- 1 root root 12884901888 Aug 21 15:37 vm10.img
-rw------- 1 qemu qemu 12884901888 Aug 21 15:51 vm11.img
[root@server1 ~]#

As you see, vm10.img has a size of exactly 12884901888 bytes. To create a logical volume of exactly the same size, we must specify -L 12884901888b (please don't forget the b at the end which tells lvcreate to use bytes - otherwise it would assume megabytes):

lvcreate -L 12884901888b -n vm10 vg_server1

Now we convert the image:

qemu-img convert /var/lib/libvirt/images/vm10.img -O raw /dev/vg_server1/vm10

Afterwards you can delete the disk image:

rm -f /var/lib/libvirt/images/vm10.img

Now we must open the guest's xml configuration file /etc/libvirt/qemu/vm10.xml...

vi /etc/libvirt/qemu/vm10.xml

... and change the following section...

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/vm10.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>

... so that it looks as follows:

    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/vg_server1/vm10'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>

Afterwards we must redefine the guest:

virsh --connect qemu:///system

define /etc/libvirt/qemu/vm10.xml

Still on the virsh shell, we can start the guest...

start vm10

... and leave the virsh shell:



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From: jfalco at: 2013-01-10 12:50:47

For step one setting SELINUX=permissive would be a better solution, so you can log denials. If you were ever required to set it to enforcing (for an audit, etc.) you would have data that you could use to change context, policies, booleans, etc. in order to allow KVM to function with SELINUX. Note: Going from =disabled to =permissive or enforcing requires a relabel on the next reboot and this will take some time.

From: Anonymous at: 2013-05-17 13:37:34

[root@localhost Downloads] sudo gedit /etc/modprobe.d/blacklist.conf

Add these below lines

blacklist kvm-amd
blacklist kvm-intel
blacklist kvm

 Save and Quit

[root@localhost Downloads]# rmmod kvm_amd
[root@localhost Downloads]# rmmod kvm