Expanding a KVM guest disk image using virt-resize

Decide on how you wish to expand the guest. Run virt-df -h and virt-list-partitions -lh on the guest disk, as shown in the following output:

# virt-df -h /dev/vg_kvm/kvm7
Filesystem                                Size       Used  Available  Use%
/dev/vg_kvm/kvm7:/dev/sda1              484.2M      48.8M     410.4M   11%
/dev/vg_kvm/kvm7:/dev/sda3               2.5G       1.3G      25.4G    5%

# virt-list-partitions -lh  /dev/vg_kvm/kvm7
/dev/sda1 ext4 500.0M
/dev/sda2 swap 1.0G
/dev/sda3 ext4 2.5G

This example we will increase the size of /dev/sda3 to 30G

1. Shutdown guest

2. Rename the original disk for the backup purpose, for lvm use lvrename command, for file use 'mv' command

# lvrename /dev/vg_kvm/kvm7 /dev/vg_kvm/kvm7.backup
  Renamed "kvm7" to "kvm7.backup" in volume group "vg_kvm"

3. Create new disk
# lvcreate -L 30G -n kvm7 vg_kvm
Logical volume "kvm7" created

4. Now resize the /dev/sda3, refer to virt-resize man for detail.

# virt-resize \

       /dev/vg_kvm/kvm7.backup /dev/vg_kvm/kvm7 \

       --expand /dev/sda3

Summary of changes:
/dev/sda1: partition will be left alone
/dev/sda2: partition will be left alone
/dev/sda3: partition will be resized from 2.5G to 28.5G
Copying /dev/sda1 ... done
Copying /dev/sda2 ... done
Copying /dev/sda3 ... done

Parition /dev/sda3 contains a filesystem or LVM PV, then this content is not automatically resized.  You can resize it afterwards either using guestfish(1) (offline) or using commands inside the guest (online resizing).

Here we resize the filesystem using guestfish

[root@kvm ~]# guestfish -a /dev/vg_kvm/kvm7

Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.

Type: 'help' for help with commands
      'quit' to quit the shell

> run
> resize2fs /dev/sda3
libguestfs: error: resize2fs: resize2fs 1.41.12 (17-May-2010)
Please run 'e2fsck -f /dev/vda3' first.
> e2fsck-f /dev/sda3
> resize2fs /dev/sda3
> exit

[root@kvm ~]# virt-df -h sl6-5
Filesystem                                Size       Used  Available  Use%
sl6-5:/dev/sda1                         484.2M      48.8M     410.4M   11%
sl6-5:/dev/sda3                          28.1G       1.3G      25.4G    5%

Try to boot the virtual machine. If it works you can delete the backup disk.

# lvchange -an vg_kvm/kvm7.backup

# lvremove vg_kvm/kvm7.backup
  Logical volume "kvm7.backup" successfully removed