The rails have changed over the years - used to be adjustable, but now most systems ship with fixed rails for a "Compaq" cabinet. You can either adjust your front and/or rear verticals (may not be on option), get third party adapters (there are a number of vendors that sell the brackets you would need), or use a shelf. There should not be a problem sitting the unit on an open shelf - the only caution is that you need to find a way to secure it so that it doesn't fall off the back when you are inserting a new drive. I have done this in the past with other storage works bays and have not had any problems.
Allan in Atlanta
