- If two drives in a raid5 disappear at the same time, then "-Af"
will add them both in rather than just one and forcing the array
to 'clean'. This is slightly safer in some cases.
+ - Check device is large enough before hot-add: this improves quality
+ of error message.
Changes Prior to 2.5.6 release
- Fix bug which meant "bitmap=xxx" in mdadm.conf was not handled