Resize disks

1. Resizing guest disk

General considerations

When you resize the disk of a VM, to avoid confusion and disasters think the process like adding or removing a disk plattern.

If you enlarge the hard disk, once you have added the disk plate your partition table and file system knows nothing about the new size, so you have to act inside the VM to fix it.

If you reduce (shrink) the hard disk, of course removing the last disk plate will probably destroy your file system and remove the data in it! So in this case is paramount to act in the VM in advance, reducing the file system and the partition size. SystemRescueCD comes very handy for it, just add it's iso as cdrom of your VM and set boot priority to CD-ROM.

qm command

You can resize your disks online or offline with command line:

qm resize <vmid> <disk> <size> 

exemple: to add 5G to your virtio0 disk on vmid100:

qm resize 100 virtio0 +5G

For virtio disks:

Linux should see the new size online without reboot with kernel >= 3.6

Windows should see the new size online without reboot with last virtio drivers.

for virtio-iscsi disk:

Linux should see the new size online without reboot with kernel >= 3.7

Windows should see the new size online without reboot with last virtio drivers.

2. Enlarge the partition(s) in the virtual disk

Depending on the installed guest there is several diffent ways to resize the partions

Windows Guests

• Guest is Windows 7, Windows Vista or Windows Server 2008
  
• Boot the system, logon as administrator and extend the disk and filesystem (Using Disk manager)
  
• For more info www.petri.co.il/extend-disk-partition-vista-windows-server-2008.htm
  

Other guests

Use gparted or similar tool (recommended)
In gparted and possibly most other tools, LVM and Windows dynamic disc is not supported

Boot the virtual machine with gparted or similar tool, enlarge the partion and optionally the file system. With som linux clients you often need to enlarge the extended partion, move the swappartion, shrink the extended partion and enlarge the root partion. (or simple delete the swap and partion andre create it again - but remember to activwate the swap agin (last step).
Gparted have some warnings about some specific operations not well supported with windows guest - outside the scope of this document but read the warnings in gparted.

Linux guests - online resizing

Enlarge the partions with gnu-cfdisk on the virtual master server, then online resize the filesystem in the virtual machine. A bit more complicated but possible faster.
AFAIK only reasonable option with guests using LVM

Install gnu-cfdisk on the virtual master

apt-get install gnu-cfdisk

Mount the disk and open CFDISK:

In case of a QCOW2 image

apt-get install nbd-client
qemu-nbd --connnect /dev/nbd0 diskimage
cfdisk /dev/nbd0

In case of a “RAW” image

cfdisk diskimage

In case of a LVM image

cfdisk /dev/xxxxx/diskimage

Enlarge the partion in CFDISK
Unfortunaly gnu-cfdisk can not resize most filesystems, only partitons - in general

• Use “fixed start” to avoid long moving time
  
• Use “change size” to only enlarge partion, not file system.
  

If the virtual guest is a linux machine with a swap disk as the last partion you can simply delete the swap, enlarge the first disk and create a new swap - but remember to “activate” the swap again (see last step)
In case of LVM guest, simple enlarge the LVM partion and mayby the extended partion

In case of QCOW2 - disconnect the NBD mount:

qemu-nbd -d /dev/nbd0

3. Enlarge the filesystem(s) in the partions on the virtual disk

If you did not resize the filesystem in step 2, you need to boot the system and online resize it.

Linux client with LVM

Enlarge the physical volume (in this case on vda5)

pvresize /dev/vda5

Enlarge the logical volume (in this case root)

lvresize -L+1G /dev/xxxx/root

Enlarge the filesystem

resize2fs /dev/xxxx/root

Linux client

Enlarge the filesystem (in this case root is on vda1)

resize2fs /dev/vda1

Optionally with linux Guests - activate the swap again

If you have deleted the swap partion with gparted or cfdisk, you need to activate it again

mkswap /dev/vdxy

where vdxy is the swap partition

Notice the UUID and maybe change it in /etc/fstab (depending on distribution)

swapon -a

check with “free” that the swap is activated