Virtualization With KVM On A Mandriva 2010.0 Server - Page 3

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Submitted by falko (Contact Author) (Forums) on Tue, 2010-03-23 18:12. ::

7 Creating An LVM-Based Guest

Mandriva 2010.0 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...

vgdisplay

[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               465.56 GB
  PE Size               4.00 MB
  Total PE              119184
  Alloc PE / Size       26420 / 103.20 GB
  Free  PE / Size       92764 / 362.36 GB
  VG UUID               aHRSbB-piY1-maoZ-OWPy-DHIy-Bl2F-MPD0y2

[root@server1 ~]#

... that contains the logical volume /dev/vg_server1/lv_root with a size of approx. 98GB and the logical volume /dev/vg_server1/lv_swap (about 5.5GB) - the rest is not allocated and can be used for KVM guests:

lvdisplay

[root@server1 ~]# lvdisplay
  --- Logical volume ---
  LV Name                /dev/vg_server1/lv_root
  VG Name                vg_server1
  LV UUID                QCl4x8-zR8r-yYZE-dNp1-leQk-ei9n-vTCcb4
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                97.66 GB
  Current LE             25000
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

  --- Logical volume ---
  LV Name                /dev/vg_server1/lv_swap
  VG Name                vg_server1
  LV UUID                rRg2Ua-WBbi-8bjn-TC0E-DBf2-Gcr2-k1nivK
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                5.55 GB
  Current LE             1420
  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/vg_server1/vm11 with a size of 20GB:

lvcreate -L20G -n vm11 vg_server1

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/vg_server1/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/vg_server1/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

Mandriva 2010.0 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/vg_server1/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 vg_server1

Now you can convert the image:

dd bs=1M if=/dev/zero of=/dev/vg_server1/vm10
qemu-img convert ~/vm10.qcow2 -O raw /dev/vg_server1/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'>
      <driver name='qemu' type='raw'/>
      <source file='/root/vm10.qcow2'/>
      <target dev='vda' bus='virtio'/>
    </disk>
[...]

... 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'/>
    </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

 

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Submitted by Anonymous (not registered) on Sat, 2010-03-27 13:50.

When starting virt-install

use the parameter:

--network=bridge:br0,mac=33:44:55:66:77:88

with a different mac for each different virtual machine. Otherwise random network errors will arise in the (normal) case of various virtual machines executing in the same hardware.
Submitted by Anonymous (not registered) on Fri, 2010-03-26 08:39.

This was a great article.  Well, I appreciate them all, but not all of them are relevant to me.  What is so nice is the thoroughness of the whole thing, its a step by step, with clear explanations, and you can follow along and do it all.
Many thanks for this, and the others too!