https://linuxconfig.org/how-to-resize-a ... e-on-linux
Expanding a disk virtual size using qemu-img
Above we saw how to reclaim unused space from a qcow2 disk image using the virt-sparsify command. In certain situations, we may want to change the virtual size of the disk image, instead, so either expand it or shrink it. Both operations are quite simple; let’s start from the former.
The easiest method we can use to expand the virtual size of a qcow2 disk image, is to use the qemu-img and the resize command. All we have to do is to provide the path of the disk and the new absolute size (or the size increment) as arguments. The current disk virtual size, as we saw, is 20GiB. Supposing we want to expand it to 30GiB, we would proceed in the following way. As a first thing we would make a backup of the current disk, just in case something goes wrong:
$ cp disk.qcow2 disk.bk.qcow2
Than, to expand the size of the image, we would run the following command:
$ qemu-img resize disk.qcow2 30G
As an alternative, instead of the final, absolute size, we could specify the size increment:
$ qemu-img resize disk.qcow2 +10G
Once the additional space has been added to the disk image we have to grow the partitions and filesystems so that they make use of it. How to proceed in order to do that depends on what partition/filesystem we want to grow. To grow the last existing partition on the disk, for example, we could just use a partitioning tool from the guest system, while it is running. For other, more complex operations, we need to adopt another strategy: shutdown the guest system and modify the disk with an “external” tool.
Modifying partitions of a disk image using NBD
Some changes to the disk image layout cannot be performed from a running system: we cannot shrink or move partitions when they are mounted, for example. In such cases, we need to modify the disk image from the host system. We can accomplish this by using the NBD protocol to connect the disk image to the host system.
Nbd stands for Network Block Device: it is a protocol which allows a machine access a block device attached to another machine. On Linux this functionality is implemented by the nbd module, which needs to be loaded:
$ sudo modprobe nbd max_part=10
In this case we loaded the module with the max_part option to specify the maximum number of partitions for the device. Once the module is loaded, to actually mount the disk image, we run the following command:
$ sudo qemu-nbd -c /dev/nbd0 disk.qcow2
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The qemu-nbdcommand is designed to export a QEMU disk image using the NBD protocol. In the example above, with the -c option we connected the filename (/dev/nbd0 in this case) to the given device: disk.qcow2. Once the disk is connected, we can use our favorite partitioning tool to modify its layout (remember to shutdown the guest system before doing any change!). For the sake of this tutorial we will use gparted:
$ gparted /dev/nbd0