This is a simple tutorial on an easy way to extend KVM virtual machine disk size. Disk usage in a VM is among the limited resources which sometimes require to be increased/reduced. It is possible to resize the disk in KVM using QEMU.
Table of Contents
Easy Way to Extend KVM Virtual Machine Disk Size
In this guide, we will use the qcow2 disk format, which is the default in KVM. Other formarts such as vmdk,qcow,cow, raw e.t.c can be extended in a similar way.
Get the Correct Name of the Domain/Virtual Machine
Before you proceed, you need to check the properties of the VM you need to extend.
Use virsh command to check the list of all running VMs so as to find the correct name of the VM/domain you need to extend the disk.
virsh list --allYou will get a list similar to the following:
Id Name State
----------------------------
15 almalinux8 running
17 opensuse runningYou can also use the GUI tool Virtual Machine Manager (VMM) to view the details/state of VMs.
Now select a VM you want to resize from list provided by the command above.
In our case, we will be extending the almalinux8 VM.
Locate Domain/Virtual Machine Disk Path
Let’s locate the disk path of the VM whose disk is to be extended using the following command:
virsh domblklist --domain almalinux8Change the last part (almalinux8) to the name of your VM.
Sample output;
Target Source
----------------------------------------------------
vda /var/lib/libvirt/images/almalinux8.qcow2
sda -Backup the Virtual Machine
I recommended that you make a backup of the virtual machine you want to the extend the disk before you can proceed to avoid loses in case of any mistake.
You can make a copy of the qcow2;
cp /var/lib/libvirt/images/almalinux8.qcow2 /home/vms/almalinux8-COPY.qcow2Or clone the current machine state and extend the disk on the cloned VM.
Check our guide on how to clone KVM Virtual Machines.
You can then power on the clone and extend the disk as follows.
Extend KVM Virtual Machine Disk Size
There are different ways in which you can extend KVM virtual machine disk size:
- Shutting down the VM, extending using
qemu-img, then start the VM to complete disk expansion. - Extending a live VM Disk
- Extending a powered-off VM Disk entirely from a host.
In this guide, we will see how to extend KVM virtual machine disk size using the first method.
- The first step is to power off the VM before moving to the next steps.
virsh shutdown --domain <vm_name>You can also use GUI to shutdown.
- Next, you need to delete the VM snapshots if there are any. Note that you have to have backed up the VM before deleting snapshots.
You can delete the snapshots from GUI or delete using the command snapshot-delete.
virsh snapshot-list --domain <vm_name>virsh snapshot-delete --domain <vm_name> --snapshotname <snapshot_name>- Check the size of the disk using fdisk
fdisk -l /var/lib/libvirt/images/almalinux8.qcow2Disk /var/lib/libvirt/images/almalinux8.qcow2: 20 GiB, 21478375424 bytes, 41949952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes- Extend the VM using qemu-img.
You can specify the ultimate size or the size you want to add preceeded by + for adding and – for reducing. If we want the ultimate size to be 30 GB, we use 30G. We can also specify +30G to mean 30GB will be added to the existing size. We are adding 10 GB in our case.
qemu-img resize /var/lib/libvirt/images/almalinux8.qcow2 +10GAgain, check the size from fdisk
fdisk -l /var/lib/libvirt/images/almalinux8.qcow2Disk /var/lib/libvirt/images/almalinux8.qcow2: 20 GiB, 21478375424 bytes, 41949952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
You can see that the disk has not increased. However, when checked with qemu-img command we note an increase in size.
qemu-img info /var/lib/libvirt/images/almalinux8.qcow2image: /var/lib/libvirt/images/almalinux8.qcow2
file format: qcow2
virtual size: 30 GiB (32212254720 bytes)
disk size: 2.91 GiB
cluster_size: 65536
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: true
refcount bits: 16
corrupt: false
extended l2: false
- Power on the VM
virsh start --domain <vm_name>Login to your VM and check the disk.
lsblk[root@localhost ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sr0 11:0 1 1024M 0 rom
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 1G 0 part /boot
└─vda2 252:2 0 19G 0 part
├─almalinux-root 253:0 0 17G 0 lvm /
└─almalinux-swap 253:1 0 2G 0 lvm [SWAP]
You can note that the total disk (vda) is 30 GB while the usable (vda1+vda2) is 20 GB.
You need to expand the disk now.
The fdisk utility will recognize the partition mismatch and will correct. Run fdisk against disk:
fdisk /dev/vda[root@localhost ~]# fdisk /dev/vda
Welcome to fdisk (util-linux 2.32.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
write p and press enter to show the partition table.
Command (m for help): p
Disk /dev/vda: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x73223988
Device Boot Start End Sectors Size Id Type
/dev/vda1 * 2048 2099199 2097152 1G 83 Linux
/dev/vda2 2099200 41943039 39843840 19G 8e Linux LVM
Note that vda2 is the partition we need to resize in this example setup.
So we need to delete it and allocate a new partition at the start of the same segment. So press d and enter.
Command (m for help): d
Partition number (1,2, default 2): 2
Partition 2 has been deleted.Then create a new partition.
Press n and enter to accept defaults for partition number, first sector and last sector.
When prompted to remove signature, enter NO.
Command (m for help): n
Partition type
p primary (1 primary, 0 extended, 3 free)
e extended (container for logical partitions)
Select (default p):
Using default response p.
Partition number (2-4, default 2):
First sector (2099200-62914559, default 2099200):
Last sector, +sectors or +size{K,M,G,T,P} (2099200-62914559, default 62914559):
Created a new partition 2 of type 'Linux' and of size 29 GiB.
Partition #2 contains a LVM2_member signature.
Do you want to remove the signature? [Y]es/[N]o: N
Commit the changes using w
Command (m for help): w
The partition table has been altered.
Syncing disks.At this point, there are two options;
- If the disk is partitioned using standard partitioning system, the disk extension is now done and you should just reboot the system.
reboot- If the disk is partitioned dynamically using Logical Volume Management system, then proceed as follows;
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sr0 11:0 1 1024M 0 rom
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 1G 0 part /boot
└─vda2 252:2 0 29G 0 part
├─almalinux-root 253:0 0 17G 0 lvm /
└─almalinux-swap 253:1 0 2G 0 lvm [SWAP]
We can now see that vda2 is ~30GB BUT the logical volume has not been extended.
To finalize the disk expansion;
- Extend the Physical Volume
- Extend the Volume Group
- Extend the logical volume
- Extend the filesystem.
Extend the physical volume;
pvsOutput;
PV VG Fmt Attr PSize PFree
/dev/vda2 almalinux lvm2 a-- <19.00g 0Next, resize the physical volume,
pvresize /dev/vda2 Physical volume "/dev/vda2" changed
1 physical volume(s) resized or updated / 0 physical volume(s) not resizedExtend volume group;
vgextend almalinux /dev/vda2Extend the logical volume to all Free space;
lvextend -l +100%FREE /dev/mapper/almalinux-rootResize the Filesystem;
If using EXT4, then;
resize2fs /dev/mapper/almalinux-rootIf using XFS, then;
xfs_growfs /dev/almalinux/root
meta-data=/dev/mapper/almalinux-root isize=512 agcount=4, agsize=1113856 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=1 bigtime=0 inobtcount=0
data = bsize=4096 blocks=4455424, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 4455424 to 7076864
Your disk should now be extended.
Confirm with the df command;
df -hT
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 636M 0 636M 0% /dev
tmpfs tmpfs 655M 0 655M 0% /dev/shm
tmpfs tmpfs 655M 8.6M 646M 2% /run
tmpfs tmpfs 655M 0 655M 0% /sys/fs/cgroup
/dev/mapper/almalinux-root xfs 27G 2.1G 25G 8% /
/dev/vda1 xfs 1014M 258M 757M 26% /boot
tmpfs tmpfs 131M 0 131M 0% /run/user/0
And that is how you can easily extend KVM virtual machine disk size.
