overspecifying raw dev size

When defining a dbspace on a raw device, is it dangerous to overspecify the size? I think after completing the "add dbspace" form (or after entering the device's pathname?), a "Verifying physical diskspace" or somesuch is flashed on the screen (and erased so darn quickly that you have to check the scroll-back buffer of your terminal emulator to see! God!) I kinda suspect that the reason why the check is done so quickly is that a seek is being done for that purpose, but can anyone from Informix tell us the exact method used? I think I tried overspecifying (way over in fact just to make sure that it's too big) and Informix didn't complain. Now, you'd ask why would one overspecify? Well, I think there are overheads and capacity specifications of all sorts and so one can't always be sure of the amount of space actually usable. Take for example, a 540M drive, now how much is there for use? 539M, 500M or what? Right now I'm always underspecifying just to be safe. But I feel kinda silly.