Virtualization With KVM On Ubuntu 11.04 - Page 3
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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 465.28 GiB
PE Size 4.00 MiB
Total PE 119112
Alloc PE / Size 24079 / 94.06 GiB
Free PE / Size 95033 / 371.22 GiB
VG UUID xGcqq6-kH4t-C3et-n31G-xb2S-1XJp-H07Apl
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 LZrfMp-DbL5-rZEl-4m1l-tyxL-53bm-gCeiTg
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 251:0
--- Logical volume ---
LV Name /dev/vg0/swap_1
VG Name vg0
LV UUID Vlwyhq-cfeh-RthB-sM6A-Tt07-Ar5G-eFGjrV
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 251:1
root@server1:~#
I will now create the virtual machine vm3 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/vm3).
mkdir -p /var/lib/libvirt/images/vm3/mytemplates/libvirt
cp /etc/vmbuilder/libvirt/* /var/lib/libvirt/images/vm3/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/vm3/vmbuilder.partition
root 8000 swap 2000 /var 10000 |
vi /var/lib/libvirt/images/vm3/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 |
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/vm3 with a size of 20GB now:
lvcreate -L20G -n vm3 vg0
We can now create the new VM as follows:
cd /var/lib/libvirt/images/vm3/
vmbuilder kvm ubuntu --suite=natty --flavour=virtual --arch=amd64 --mirror=http://de.archive.ubuntu.com/ubuntu -o --libvirt=qemu:///system --ip=192.168.0.103 --gw=192.168.0.1 --part=vmbuilder.partition --raw=/dev/mapper/vg0-vm3 --templates=mytemplates --user=administrator --name=Administrator --pass=howtoforge --addpkg=vim-nox --addpkg=unattended-upgrades --addpkg=acpid --firstboot=/var/lib/libvirt/images/vm3/boot.sh --mem=256 --hostname=vm3 --bridge=br0
Please note that I use --raw=/dev/mapper/vg0-vm3 instead of --raw=/dev/vg0/vm3 switch - both /dev/vg0/vm3 and /dev/mapper/vg0-vm3 are symlinks that point to the same logical volume - /dev/dm-2 in my case - but when I used --raw=/dev/vg0/vm3 the vmbuilder process failed with the following error message...
2011-05-05 15:53:24,056 INFO : Partition at beginning of disk - reserving first cylinder
2011-05-05 15:53:24,764 INFO : device-mapper: deps ioctl failed: No such device or address
2011-05-05 15:53:24,765 INFO : Cleaning up
2011-05-05 15:53:24,765 ERROR : Process (['parted', '--script', '--', '/dev/vg0/vm3', 'mkpart', 'primary', 'ext2', '63s', '7999']) returned -11. stdout: , stderr: device-mapper: deps ioctl failed: No such device or address
Traceback (most recent call last):
File "/usr/bin/vmbuilder", line 24, in <module>
cli.main()
File "/usr/lib/python2.7/dist-packages/VMBuilder/contrib/cli.py", line 223, in main
hypervisor.install_os()
File "/usr/lib/python2.7/dist-packages/VMBuilder/hypervisor.py", line 65, in install_os
self.call_hooks('mount_partitions', self.chroot_dir)
File "/usr/lib/python2.7/dist-packages/VMBuilder/distro.py", line 67, in call_hooks
call_hooks(self, *args, **kwargs)
File "/usr/lib/python2.7/dist-packages/VMBuilder/util.py", line 165, in call_hooks
getattr(context, func, log_no_such_method)(*args, **kwargs)
File "/usr/lib/python2.7/dist-packages/VMBuilder/hypervisor.py", line 88, in mount_partitions
disk.partition()
File "/usr/lib/python2.7/dist-packages/VMBuilder/disk.py", line 117, in partition
part.create(self)
File "/usr/lib/python2.7/dist-packages/VMBuilder/disk.py", line 295, in create
run_cmd('parted', '--script', '--', disk.filename, 'mkpart', 'primary', self.parted_fstype(), partition_start, self.end)
File "/usr/lib/python2.7/dist-packages/VMBuilder/util.py", line 120, in run_cmd
raise VMBuilderException, "Process (%s) returned %d. stdout: %s, stderr: %s" % (args.__repr__(), status, mystdout.buf, mystderr.buf)
VMBuilder.exception.VMBuilderException: Process (['parted', '--script', '--', '/dev/vg0/vm3', 'mkpart', 'primary', 'ext2', '63s', '7999']) returned -11. stdout: , stderr: device-mapper: deps ioctl failed: No such device or address
root@server1:/var/lib/libvirt/images/vm3#
... while it succeeded with --raw=/dev/mapper/vg0-vm3 (I tested this multiple times). This looks like a bug in vmbuilder or parted to me.
You can now use virsh to manage the VM:
virsh --connect qemu:///system
Run the define command first...
define /etc/libvirt/qemu/vm3.xml
... before you start the VM:
start vm3
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/
