QUOTE (Jack Flesher @ Dec 10 2008, 11:57 PM)

As for your HP unit, a few questions: If one drive in the array fails, what happens to your data?
It should be still there if set up properly.
QUOTE
After that failure can you replace the failed drive with ANY drive, or do you have to use an identical drive to the rest in the array?
Just one as big as the failed drive.
The main difference bewtween the WHS and the Drobo is one works well with Windows and not Macs [WHS] and one works with both [the Drobo].
However if you have problems with data recovery, one is on a system by MS [so lots of support] and one is on a system that is proprietry and by a small company who could easily vanish.
I was quite annoyed to find WHS doesn't back up OSX/HFS, as the adverts said they work with OSX. They didn't mention it was very limited.
It's Apple's fault why as to why it cannot be used for Time Machine, but as there no OSX drivers to run WHS in OSX, MS or HP are even more to blame [in the HP WHS].