Resize a KVM VM disk¶

Part of the KVM overview. Grow a disk from the host, then grow the partition, LVM and filesystem inside the guest.

Growing is safe; shrinking is not (do not, unless you have shrunk the filesystem and partitions first and have a backup).

Step 1: grow the image (host)¶

Offline (+ grows by an amount):

virsh shutdown vm01
qemu-img resize /var/lib/libvirt/images/vm01.qcow2 +30G
virsh start vm01

Online (a running VM). This sets the new total size, it does not add to the old size:

virsh domblklist vm01
virsh blockresize vm01 vda 50G

Confirm the guest saw it: dmesg -T | grep -E 'virtio_blk|capacity change' and lsblk.

Step 2: grow the partition (guest)¶

lsblk
sudo growpart /dev/vda 1          # package: cloud-guest-utils (Debian) / cloud-utils-growpart (RHEL)

Step 3a: no LVM, grow the filesystem¶

sudo resize2fs /dev/vda1          # ext4
sudo xfs_growfs /                 # xfs (takes the mount point)

Step 3b: LVM¶

The physical volume lives on a partition, so the partition must be grown first (step 2, on the partition that holds the PV, e.g. growpart /dev/vda 3). Rebooting alone will not make LVM see new disk space. Then:

sudo pvresize /dev/vda3
sudo lvextend -r -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv    # -r also grows the filesystem

Without -r, run resize2fs / xfs_growfs on the logical volume afterwards.

References: How-To Geek, sandilands.info (LVM)

Windows guests¶

Shut down, qemu-img resize disk.qcow2 +10G, start, then Disk Management → right-click the volume → Extend Volume.