I have two suggestion that I think would be pretty easy to implement. Both would probably be added to the "edit rack" configuration page.

1. Add a field to specify number of power connectors

2. Add a field to specify maximum depth of the case

With suggestion 2, you'd know immediately if a module was too deep for your case. The system tells you the depth of your deepest module, but it doesn't tell you specifically which one it is. If the system had depth logic, it could warn you as you add them.

With suggestion 1, you'd also know if you had too many powered modules for your case. Just because 21 4HP modules will fit in an 84HP case, doesn't mean there's enough power connectors for all of them. If 6 or 7 were passive modules, it may still work.

Anyway, just a little thing I noticed. I love the site overall. A+++