Virtualization With KVM On A Fedora 10 Server - Page 3
7 Creating An LVM-Based Guest
Fedora 10 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/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 GB
PE Size 4.00 MB
Total PE 119112
Alloc PE / Size 59842 / 233.76 GB
Free PE / Size 59270 / 231.52 GB
VG UUID Uxz7c6-Dt9m-r3Iw-zgeA-Esl1-T6Qt-iEigVb
[root@server1 ~]#
... that contains the logical volume /dev/vg0/root with a size of approx. 232GB and the logical volume /dev/vg0/swap_1 (about 1GB) - the rest is not allocated and can be used for KVM guests:
lvdisplay
[root@server1 ~]# lvdisplay
--- Logical volume ---
LV Name /dev/vg0/root
VG Name vg0
LV UUID 4pcUKQ-rRa8-qo7Q-XbFS-I8t0-Qhm5-OotSYV
LV Write Access read/write
LV Status available
# open 1
LV Size 232.83 GB
Current LE 59604
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0
--- Logical volume ---
LV Name /dev/vg0/swap_1
VG Name vg0
LV UUID 6JPk1y-yIQs-pPat-P9lR-6DWr-jLFf-K0Jhpv
LV Write Access read/write
LV Status available
# open 1
LV Size 952.00 MB
Current LE 238
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 vm11 as an LVM-based guest. I want vm11 to have 20GB of disk space, so I create the logical volume /dev/vg0/vm11 with a size of 20GB:
lvcreate -L20G -n vm11 vg0
Afterwards, we use the virt-install command again to create the guest:
virt-install --connect qemu:///system -n vm11 -r 512 --vcpus=2 --disk path=/dev/vg0/vm11 -c ~/debian-500-amd64-netinst.iso --vnc --noautoconsole --os-type linux --os-variant debianLenny --accelerate --network=bridge:br0 --hvm
Please note that instead of -f ~/vm11.qcow2 I use --disk path=/dev/vg0/vm11, and I don't need the -s switch to define the disk space anymore because the disk space is defined by the size of the logical volume vm11 (20GB).
Now follow chapter 5 to install that guest.
8 Converting Image-Based Guests To LVM-Based Guests
Fedora 10 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
quit
Then create a logical volume (e.g. /dev/vg0/vm10) that has the same size as the image file - the image has 12GB, so the logical volume must have 12GB of size as well:
lvcreate -L12G -n vm10 vg0
Now you can convert the image:
qemu-img convert ~/vm10.qcow2 -O raw /dev/vg0/vm10
Afterwards you can delete the disk image:
rm -f ~/vm10.qcow2
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'> <source file='/root/vm10.qcow2'/> <target dev='hda' bus='ide'/> </disk> [...] |
... so that it looks as follows:
[...] <disk type='file' device='disk'> <source file='/dev/vg0/vm10'/> <target dev='hda' bus='ide'/> </disk> [...] |
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:
quit
9 Links
- KVM: http://kvm.qumranet.com/
- Fedora: http://fedoraproject.org/
- Debian: http://www.debian.org/
- Ubuntu: http://www.ubuntu.com/