6 Creating An LVM-Based VM
LVM-based VMs have some advantages over image-based VMs. They are not as heavy on hard disk IO, and they are easier to back up (using LVM snapshots).
To use LVM-based VMs, 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/vg0 with a size of approx. 465GB...
vgdisplay
root@server1:~# vgdisplay
--- Volume group ---
VG Name vg0
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 465.29 GiB
PE Size 4.00 MiB
Total PE 119115
Alloc PE / Size 24079 / 94.06 GiB
Free PE / Size 95036 / 371.23 GiB
VG UUID PRenhH-0MvN-wXCL-nl4i-IfsQ-J6fc-2raYLD
root@server1:~#
... that contains the logical volumes /dev/vg0/root with a size of approx. 100GB and /dev/vg0/swap_1 with a size of 1GB - the rest is not allocated and can be used for VMs:
lvdisplay
root@server1:~# lvdisplay
--- Logical volume ---
LV Name /dev/vg0/root
VG Name vg0
LV UUID dwnORf-yG3U-x1ZC-Bet1-TOoc-q1Dd-KZnbtw
LV Write Access read/write
LV Status available
# open 1
LV Size 93.13 GiB
Current LE 23841
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:0
--- Logical volume ---
LV Name /dev/vg0/swap_1
VG Name vg0
LV UUID ZdPKO6-sZrr-tIRb-PPcl-aWBj-QAUU-fnYUuP
LV Write Access read/write
LV Status available
# open 2
LV Size 952.00 MiB
Current LE 238
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:1
root@server1:~#
I will now create the virtual machine vm5 as an LVM-based VM. We can use the vmbuilder command again. vmbuilder knows the --raw option which allows to write the VM to a block device (e.g. /dev/vg0/vm5) - I've tried this, and it gave back no errors, however, I was not able to boot the VM (start vm5 didn't show any errors either, but I've never been able to access the VM). Therefore, I will create vm5 as an image-based VM first and then convert it into an LVM-based VM.
mkdir -p /var/lib/libvirt/images/vm5/mytemplates/libvirt
cp /etc/vmbuilder/libvirt/* /var/lib/libvirt/images/vm5/mytemplates/libvirt/
Make sure that you create all partitions in just one image file, so don't use --- in the vmbuilder.partition file:
vi /var/lib/libvirt/images/vm5/vmbuilder.partition
root 8000 swap 2000 /var 10000 |
vi /var/lib/libvirt/images/vm5/boot.sh
# This script will run the first time the virtual machine boots # It is ran as root. # Expire the user account passwd -e administrator # Install openssh-server apt-get update apt-get install -qqy --force-yes openssh-server |
cd /var/lib/libvirt/images/vm5/
vmbuilder kvm ubuntu --suite=quantal --flavour=virtual --arch=amd64 --mirror=http://de.archive.ubuntu.com/ubuntu -o --libvirt=qemu:///system --ip=192.168.0.105 --gw=192.168.0.1 --part=vmbuilder.partition --templates=mytemplates --user=administrator --name=Administrator --pass=howtoforge --addpkg=vim-nox --addpkg=unattended-upgrades --addpkg=acpid --addpkg=linux-image-generic --firstboot=/var/lib/libvirt/images/vm5/boot.sh --mem=512 --hostname=vm5 --bridge=br0
As you see from the vmbuilder.partition file, the VM will use a max. of 20GB, so we create a logical volume called /dev/vg0/vm5 with a size of 20GB now:
lvcreate -L20G -n vm5 vg0
Don't create a file system in the new logical volume!
We will use the qemu-img command to convert the image to an LVM-based VM.
Now we go to the VM's ubuntu-kvm/ directory...
cd /var/lib/libvirt/images/vm5/ubuntu-kvm/
... and find out how our image is named:
ls -l
root@server1:/var/lib/libvirt/images/vm5/ubuntu-kvm# ls -l
total 592140
-rw-r--r-- 1 root root 606470144 Nov 9 20:06 tmpesHsUI.qcow2
root@server1:/var/lib/libvirt/images/vm5/ubuntu-kvm#
Now that we know the name of our image (tmpN27tbO.qcow2), we can convert it as follows:
qemu-img convert tmpesHsUI.qcow2 -O raw /dev/vg0/vm5
Afterwards you can delete the disk image:
rm -f tmpesHsUI.qcow2
Now we must modify the VM's configuration...
virsh edit vm5
... and change the following section...
[...] <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/libvirt/images/vm5/ubuntu-kvm/tmpesHsUI.qcow2'/> <target dev='hda' bus='ide'/> <address type='drive' controller='0' bus='0' unit='0'/> </disk> [...] |
... so that it looks as follows:
[...] <disk type='file' device='disk'> <driver name='qemu' type='raw'/> <source file='/dev/vg0/vm5'/> <target dev='hda' bus='ide'/> <address type='drive' controller='0' bus='0' unit='0'/> </disk> [...] |
You can now use virsh to manage the VM:
virsh --connect qemu:///system
Because we have modified the VM's XML file, we must run the define command first...
define /etc/libvirt/qemu/vm5.xml
... before we start the VM:
start vm5
7 Links
- KVM (Ubuntu Community Documentation): https://help.ubuntu.com/community/KVM
- vmbuilder: https://help.ubuntu.com/community/JeOSVMBuilder
- JeOS and vmbuilder: http://doc.ubuntu.com/ubuntu/serverguide/C/jeos-and-vmbuilder.html
- Ubuntu: http://www.ubuntu.com/