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

[[email protected] ~]# 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

[[email protected] ~]#

... 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

[[email protected] ~]# 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

[[email protected] ~]#

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

 

Falko Timme

About Falko Timme

Falko Timme is an experienced Linux administrator and founder of Timme Hosting, a leading nginx business hosting company in Germany. He is one of the most active authors on HowtoForge since 2005 and one of the core developers of ISPConfig since 2000. He has also contributed to the O'Reilly book "Linux System Administration".

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By: dyasny

nice HOWTO, but basically, on a regular installation of F10, running GNOME, this is all achievable by simply installing libvirt and the rest of the virtualization package.

the only thing I could not achieve  on my F10 box was setting up SDL instead of VNC