Looks like you’re safe as long as you remember your password.

I’m assuming this is the product: http://www.iomagic.com/Products/show_all_results.asp?ProdID=I250HD35 — it looks like this product uses encryption in order to secure the data stored on the external hard drives from prying eyes. If you had to enter a password when you were first setting up your vaults, my guess is that you should still have access to the data on the drive after you reinstall the product software. If you really want to be 100% sure, though, take it to another computer, install the software, and see if you get access to your files. If not, don’t reinstall the OS without backing up the data elsewhere. I’m guessing you’ll be fine, though: there’s no real point of external backup if you can’t use it without the original OS intact.