How to re-size partitions in a complete hard drive image

QEMU comes with the qemu-img program to convert between image formats.

qemu-img convert -f qcow2 -O raw my-qcow2.img /dev/sdb

There is better alternative than dd to extend a file. The dd command requires several parameters to run properly (to not corrupt your data). I use truncate instead. Despite of its name it can extend the size of a file as well:

truncate - shrink or extend the size of a file to the specified size

-s, --size=SIZE

set or adjust the file size by SIZE

SIZE is an integer and optional unit (example: 10M is 10*1024*1024). Units > are K, M, G, T, P, E, Z, Y (powers of 1024) or KB, MB, ... (powers of 1000).

SIZE may also be prefixed by one of the following modifying characters: '+' extend by, '-' reduce by, '<' at most, '>' at least, '/' round down to multiple of, '%' round up to multiple of.

thus,

truncate -s +1G MyDrive.vhd

safely expands your file by 1 gigabyte. And, yes, it does sparse expansion when supported by the underlying filesystem, so the actual blocks would be allocated on demand.

When a file is expanded, don't forget to run resize2fs:

resize2fs MyDrive.vhd

Also, the whole thing may be done online (without umount'ing the device) for file systems that support online resize:

losetup -c loopdev

updates in-kernel information on a backing file,

and

 resize2fs loopdev

resizes the mounted file system online