How to Resize KVM Virtual Machine disk size

Only images in raw format can be resized in both directions, whereas qcow2 images can be grown but cannot be shrunk.

Confirm the original disk information.

~]# virsh dumpxml vm2 | sed -n '/disk type/,/\/disk/p'
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/vm2.qcow2'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </disk>

~]# virsh domblklist vm2
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/vm2.qcow2

~]# qemu-img info /var/lib/libvirt/images/vm2.qcow2
image: /var/lib/libvirt/images/vm2.qcow2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 1.6G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true

Resize the disk.

a) Method 1: Using virsh blockresize (Recommended)

~]# virsh blockresize vm2 vda 15G
Block device 'vda' is resized

b) Method 2: Using qemu-img

~]# qemu-img resize /var/lib/libvirt/images/vm2.qcow2 +1G
ERROR cluster 163874 refcount=0 reference=1
Rebuilding refcount structure
Repairing cluster 1 refcount=1 reference=0
Repairing cluster 2 refcount=1 reference=0
Repairing cluster 32776 refcount=1 reference=0
Repairing cluster 65549 refcount=1 reference=0
Repairing cluster 98322 refcount=1 reference=0
Repairing cluster 131095 refcount=1 reference=0
Repairing cluster 163868 refcount=1 reference=0
Image resized.

~]# virsh qemu-monitor-command vm2 --hmp "info block"
drive-virtio-disk0: removable=0 io-status=ok file=/var/lib/libvirt/images/vm2.qcow2 ro=0 drv=qcow2 encrypted=0 bps=0 bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0

~]# virsh qemu-monitor-command vm2 --hmp "block_resize drive-virtio-disk0 16G"