RAID5 capacities / usable drive space ...

[The Hermit Hacker]

I have someone telling me something that I'd never heard before, and find
difficult to believe ...

Apparently, he is under the impression that altho a file system shows a
capacity of, say, 100G, its usable space is around 50% of that ...
anything higher then that, you risk problems ... (significantly reduced
MTBF of the drives, degradation in performance, etc) ...

His opinion seems to be based on some talks he had with ppl at IBM and
Seagate way back in '89, but still seems to feel they are applicable today
...

Is there any fact behind his opinion?  If not, anything I can point him at
to read?  If so, anything I can be pointed at to read?

Thanks ...

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy at hub.org           secondary: scrappy@{freebsd|postgresql}.org