wiki/gofurther/resize.md

title	description	published	date	tags	editor	dateCreated
Resize an existing virtual disk		true	2024-07-13T13:33:59.560Z		markdown	2021-11-13T11:41:29.087Z

Resize a disk

Background

A virtual machine's disk may have to be resized, typically due to lack of space. This page explains how to do so.

Usage for Linux guests

In-place expansion is not supported. A new disk of the desired size has to be created. {.is-info}

• Navigate to the location that contains the existing image

cd /var/lib/libvirt/images

• Create a new blank disk image of the desired size

Use the following command to create a disk of 20 GB called guest_20G.img.

qemu-img create -f raw guest_20G.img 20G

• Identify the filesystem layout of the existing disk guest.img

# virt-filesystems -a -l -h guest.img
Name       Type        VFS   Label  Size        Parent
/dev/vda1  filesystem  vfat  EFI    133935104   -
/dev/vda2  filesystem  ext4  boot   366869504   -
/dev/vda3  filesystem  ext4  root   9933475840  -

One can tell that the root partition is located under /dev/vda3. This is the one that will need to be expanded.

• Copy the formet old data to the new disk and expand the root partition of the said disk

This command is cabable of expanding different kinds of filesystems, including ext4 and btrfs
{.is-info}

# virt-resize --expand /dev/vda3 guest.img guest_20G.img

• Review the changes

[   0.0] Examining guest_20G.img
**********

Summary of changes:

/dev/vda1: This partition will be left alone.

/dev/vda2: This partition will be left alone.

/dev/vda3: This partition will be resized from 10G to 20G.  The 
filesystem ext4 on /dev/vda3 will be expanded using the ‘resize2fs’ 
method.

**********
[   2.1] Setting up initial partition table on guest_20G.img
[  12.9] Copying /dev/vda1
[  13.1] Copying /dev/vda2
[  13.4] Copying /dev/vda3
 100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
[  38.3] Expanding /dev/vda3 using the ‘resize2fs’ method

Resize operation completed with no errors.  Before deleting the old disk, 
carefully check that the resized disk boots and works correctly.

• Switch to the new disk for your virtual machine

Now that the new disk has been created, it can be used in the virtual machine.

# virsh edit guest

Locate the source line for the existing disk guest.img:

[...]
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
      <source file='/var/lib/libvirt/images/guest.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </disk>
[...]

Edit the said line so that it points to the new disk guest-20G.img:

[...]
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
      <source file='/var/lib/libvirt/images/guest-20G.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </disk>
[...]

Start the virtual machine and ensure that it is working properly. If it does, the former disk could be removed.

Resources

As per the software description : "qemu-img allows you to create, convert and modify images offline. It can handle all image formats supported by QEMU."

• Installation

On Fedora-related distributions, virt-resize is provided by the guestfs-tools package :

# dnf install guestfs-tools

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