e2fsck -f disk1.raw
tune2fs -f -E clear_mmp disk1.raw
resize2fs -M disk1.raw 20G
truncate -s 20G disk1.raw
resize2fs disk1.raw
mcedit /etc/pve/nodes/pve/lxc/102.conf
... rootfs: local:xxx/disk1.raw,size=20G ...