= How do I extend the disk space for a KVM guest? =

Each guest is running logical volume manager. If you need to allocate more disk space on a guest, run the vgs command to determine if you already have un-allocated disk space available.

This example shows that chavez has space available:

{{{
0 chavez:~# vgs
  VG         #PV #LV #SN Attr   VSize   VFree 
  vg_chavez0   1   7   0 wz--n- 499.52g 57.52g
0 chavez:~#
}}}

There's no need to allocate more space from the host, since chavez already has 57GB free.

Here's an example of a host without any available disk space:

{{{
0 mandela:~# vgs
  VG          #PV #LV #SN Attr   VSize  VFree
  vg_mandela0   1   6   0 wz--n- 69.52g    0 
0 mandela:~#
}}}

mandela has no available disk space, so additional space must be allocated from the host, ken.

Our KVM guests are each allocated a single logical volume from the KVM host's volume group (typically named after the host).

The first and easiest step is to login to the host, check available disk space:

{{{
0 ken:~# vgs
  VG      #PV #LV #SN Attr   VSize VFree
  vg_ken0   1  16   0 wz--n- 1.82t 1.29t
0 ken:~# 
}}}

ken has 1.29 TB available.

Next check how much space is already allocated to your guest:

{{{
0 ken:~# lvs | grep mandela 
  mandela  vg_ken0 -wi-ao  20.00g                                      
0 ken:~#
}}}

The, add more space:

{{{
lvextend --size 35G vg_ken0/mandela
  Extending logical volume mandela to 35.00 GiB
  Logical volume mandela successfully resized
0 ken:~#
}}}

Next, you will need to reboot the guest before the change in disk space is recognized by the guest ([http://comments.gmane.org/gmane.comp.emulators.kvm.devel/64203 this is apparently a requirement until someone implements online disk resizing]).  You will need to execute: `shutdown -h now`, so that the underlying block devices get reinitialized by a new process.

After rebooting, you can confirm the new size on the guest by running:

{{{
cat /proc/partitions
}}}

You should see that the base disk (e.g. /dev/vda) reflects the new size, although all of the partitions reflect their old sizes (e.g. /dev/vda2).

Next, on the guest, run parted and print the current partition table. It's often easier to manage if you look at units in sectors:

{{{
parted /dev/vda unit s p
}}}

Note carefully the start sector for the last partition. You will need this exact number in the step below.

Delete the last partition, and re-create it with a higher end sector (yes, you can do this without destroying the data on the disk). Replace STARTSECTOR with the start sector of the output from the command above. Specifying -1 as the end sector means go as far to the end as possible. If you get a message saying that the sector you requested is not possible, accept a different one, you can safely say yes.

{{{
parted /dev/vda
}}}

The following commands are executed in interactive mode:

{{{
unit s
rm 2
mkpart primary STARTSECTOR -1 
}}}

Next, check to see if your changes are reflected in /proc/partitions:

{{{
cat /proc/partitions
}}}

You may need to reboot a second time before they will show up.

Once your partition table is reflecting the new size, run the following command:

{{{
pvresize /dev/vda2
}}}

And now your volume group should show additional free space.