Comparing options for Xen file-based storage

I’ve concluded that file-based storage for hard disk images is more convenient from a management perspective than using LVM. However, even if one decides to go the route of using files there is still the question of which format to use. Xen supports several options at the moment with more to come (hopefully).

Raw disk image

• How to create 4GB image:
  • dd count=1M bs=4K if=/dev/zero of=raw.img

Sparse disk image

• How to create 4GB image:
  • dd count=0 bs=4K seek=1M if=/dev/zero of=sparse.img

Qcow disk image

• How to create 4GB image:
  • qcow-create 4096 qcow.img

Comparisons

In my testing both sparse images and qcow images are simply too slow for use. Only raw images are fast enough. This may change if Xen incorporates all of the file handling options from Qemu. If that happens than Xen will have even more options, some of which may be fast enough to use while providing benefits missing from raw images.