These were the basic steps I had to go through to resize a partition inside of a DRBD disk device.  I think a similar procedure would be needed to resize the disk inside a file based disk image.

• Check the partition info using parted’s “print” command

Number  Start   End     Size    Type     File system  Flags
1      32.3kB  107MB   107MB   primary  ext3              
2      107MB   625MB   518MB   primary  linux-swap        
3      625MB   6926MB  6301MB  primary  ext3

In this case I wanted to resize partition #3, since it was on a 10GB device with free space behind it.

• Use kpartx to make the individual partitions in the device accessible: kpartx -a /dev/drbd1
  • This makes it so you can access the partitions at: /dev/mapper/drbd1p#
• Check the file system: e2fsck -f -v /dev/mapper/drbd1p3
• Convert to ext2 FS: tune2fs -O ^has_journal /dev/mapper/drbd1p3
• Resize the partition — I couldn’t use the resize command in parted properly, so instead I deleted the partition, then recreated it.  Make sure you write down the start point!
• Convert back to ext3: tune2fs -j /dev/mapper/drbd1p3
• Rerun the e2fsck command to double check it
• I think that’s it