Create a new image file (10GiB):
dd if=/dev/zero of=mailstore.img bs=1M count=10k
(Note: You can also create a sparse file with dd’s seek option. Have a look at the dd manpage or the examples on http://en.wikipedia.org/wiki/Dd_(Unix))
Create the new filesystem:
mkfs.ext3 mailstore.img
Label the filesystem:
e2label mailstore.img <new-label>
Edit the DomU’s config file, /etc/xen/<hostname>.cfg
and add the new disk:
disk = [ "tap:aio:/vm/disk.img,xvda,w", \ "tap:aio:/vm/mailstore.img,xvdb,w" ]
Start the VM:
xm create <hostname>.cfg
Edit DomU’s /etc/fstab
& mount the disk:
[...] LABEL=/<new-label> /<mount-point> ext3 defaults 0 1 [...]