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Jose Roman Martin Gil
Jose Roman Martin Gil

Posted on • Originally published at blog.jromanmartin.io on

๐Ÿ–ญ How to resize a virtual disk

#community #productivity #tools #howto

If you work with VMs it is very common that sometimes you need more space, but your VMs were defined with an estimated size. I started to use Virtual Machine Manager to manage my VMs when I joined to Red Hat (sorry but in my previous life I usually used Oracle VM VirtualBox) and sometimes I need to resize my image files but I didnโ€™t know how to do it.

Thanks to Oscar Arribas Arribas I learned to do it using a fewvirt-xxx commands. It is very possible to do it using other commands/steps/alternatives however this way is good for me.

Step 0๏ธโƒฃ - Checking current VM disk size

Inside of your VM you can check the size of the each disk with the df command:

[rhmw@f38mw01 ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 4.0M 0 4.0M 0% /dev
tmpfs 977M 0 977M 0% /dev/shm
tmpfs 391M 1.3M 390M 1% /run
/dev/vda3 19G 4.7G 14G 26% /
tmpfs 977M 40K 977M 1% /tmp
/dev/vda3 19G 4.7G 14G 26% /home
/dev/vda2 974M 257M 650M 29% /boot
tmpfs 196M 56K 196M 1% /run/user/42
tmpfs 196M 40K 196M 1% /run/user/1000
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Here the home has 20G allocated. I would like to extend it to 40G.

Step 1๏ธโƒฃ - Creating a new disk image

Your VM must be stopped before starting to resize it using a new disk image with the desired size.

We can create a new disk using the qemu-img tool, something like this:

on ๐ŸŽฉ โฏ qemu-img create -f qcow2 f38mw01-resized.qcow2 40G
Formatting 'f38mw01-resized.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=42949672960 lazy_refcounts=off refcount_bits=16
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Or creating the new image file by the Storage tab in the virt-manager Connection Details option (Edit -> Connection Details):

Step 2๏ธโƒฃ - Renaming the old disk image

Rename the old image file as a backup file (it could be needed to use in a roll-back case):

mv f38mw01.qcow2 f38mw01.qcow2.backup
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You can also describe the file systems in the old image file:

on ๐ŸŽฉ โฏ sudo virt-filesystems --long -h --all -a f38mw01.qcow2.backup
Name Type VFS Label MBR Size Parent
/dev/sda1 filesystem unknown - - 1.0M -
/dev/sda2 filesystem ext4 - - 973M -
/dev/sda3 filesystem btrfs fedora_localhost-live - 19G -
btrfsvol:/dev/sda3/home filesystem btrfs fedora_localhost-live - - -
btrfsvol:/dev/sda3/root filesystem btrfs fedora_localhost-live - - -
btrfsvol:/dev/sda3/root/var/lib/machines filesystem btrfs fedora_localhost-live - - -
/dev/sda1 partition - - - 1.0M /dev/sda
/dev/sda2 partition - - - 1.0G /dev/sda
/dev/sda3 partition - - - 19G /dev/sda
/dev/sda device - - - 20G -
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Step 3๏ธโƒฃ - Truncating the new disk image

Truncate the old image file and resize the new image file with the new space:

on ๐ŸŽฉ โฏ sudo truncate -r f38mw01.qcow2.backup f38mw01-resized.qcow2
on ๐ŸŽฉ โฏ sudo truncate -s +20G f38mw01-resized.qcow2
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Step 4๏ธโƒฃ - Expanding the new disk image

Expand the new image file using as base the old image file. In this step I am expanding the physical disk mounted for the home folder.

on ๐ŸŽฉ โฏ sudo virt-resize --expand /dev/sda3 f38mw01.qcow2.backup f38mw01-resized.qcow2
[0.0] Examining f38mw01.qcow2.backup
**********

Summary of changes:

virt-resize: /dev/sda1: This partition will be left alone.

virt-resize: /dev/sda2: This partition will be left alone.

virt-resize: /dev/sda3: This partition will be resized from 19.0G to 39.0G. 
 The filesystem btrfs on /dev/sda3 will be expanded using the 
โ€˜btrfs-filesystem-resizeโ€™ method.

**********
[2.6] Setting up initial partition table on f38mw01-resized.qcow2
[13.4] Copying /dev/sda1
[13.4] Copying /dev/sda2
 100% โŸฆโ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โŸง --:--
[15.8] Copying /dev/sda3
 100% โŸฆโ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โŸง 00:00
[48.0] Expanding /dev/sda3 using the โ€˜btrfs-filesystem-resizeโ€™ method

virt-resize: Resize operation completed with no errors. Before deleting 
the old disk, carefully check that the resized disk boots and works 
correctly.
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Step 5๏ธโƒฃ - Starting the VM with the new disk image

Rename the new disk image as the original one used by the VM:

on ๐ŸŽฉ โฏ mv f38mw01-resized.qcow2 f38mw01.qcow2
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Start the VM and the check that our home has more space:

[rhmw@f38mw01 ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 4.0M 0 4.0M 0% /dev
tmpfs 977M 0 977M 0% /dev/shm
tmpfs 391M 1.3M 390M 1% /run
/dev/vda3 39G 4.7G 34G 13% /
tmpfs 977M 40K 977M 1% /tmp
/dev/vda2 974M 257M 650M 29% /boot
/dev/vda3 39G 4.7G 34G 13% /home
tmpfs 196M 56K 196M 1% /run/user/42
tmpfs 196M 40K 196M 1% /run/user/1000
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The /dev/vda3 now is 34G (in the step 0, the size was 19G). Great!!!

Bonus Track ๐Ÿ’ก - Resizing Microsoft Windows VMs

I know, I know what you are thinking ๐Ÿค” โ€ฆ this stuff works because I am using a Linux OS ๐Ÿ˜‡. However, this process also works for Windows VMs.

Here an example of a Windows 10 with a hard disk of 40G to extend to 50G:

The process is exactly the same:

Create new disk image:

on ๐ŸŽฉ โฏ qemu-img create -f qcow2 win10-resized.qcow2 50G
Formatting 'win10-resized.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=53687091200 lazy_refcounts=off refcount_bits=16
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Back the original disk image:

on ๐ŸŽฉ โฏ mv win10.qcow2 win10.qcow2.backup
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Check the file systems of the old image:

on ๐ŸŽฉ โฏ sudo virt-filesystems --long -h --all -a win10.qcow2.backup 
Name Type VFS Label MBR Size Parent
/dev/sda1 filesystem ntfs System Reserved - 579M -
/dev/sda2 filesystem ntfs - - 39G -
/dev/sda1 partition - - 07 579M /dev/sda
/dev/sda2 partition - - 07 39G /dev/sda
/dev/sda device - - - 40G -
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Truncate the new disk image:

on ๐ŸŽฉ โฏ sudo truncate -r win10.qcow2.backup win10-resized.qcow2 
on ๐ŸŽฉ โฏ sudo truncate -s +10G win10-resized.qcow2
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Expand the new disk image:

on ๐ŸŽฉ โฏ sudo virt-resize --expand /dev/sda2 win10.qcow2.backup win10-resized.qcow2 
[0.0] Examining win10.qcow2.backup
**********

Summary of changes:

virt-resize: /dev/sda1: This partition will be left alone.

virt-resize: /dev/sda2: This partition will be resized from 39.4G to 49.4G. 
 The filesystem ntfs on /dev/sda2 will be expanded using the 
โ€˜ntfsresizeโ€™ method.

**********
[1.9] Setting up initial partition table on win10-resized.qcow2
[2.8] Copying /dev/sda1
[3.6] Copying /dev/sda2
 100% โŸฆโ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โ–’โŸง 00:00
[55.7] Expanding /dev/sda2 using the โ€˜ntfsresizeโ€™ method

virt-resize: Resize operation completed with no errors. Before deleting 
the old disk, carefully check that the resized disk boots and works 
correctly.
Enter fullscreen mode Exit fullscreen mode

Rename the new disk using the original name

on ๐ŸŽฉ โฏ mv win10-resized.qcow2 win10.qcow2
Enter fullscreen mode Exit fullscreen mode

Start the VM and check the new disk size:

๐Ÿšฉ Happy resizing!!! ๐Ÿค–

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