You can set up a seperate raid1 mirror that can do that for you. Search these forums for raid and raid1 and you will find your answer.
I have my SME installed on a single disk, then I created a 300gb raid1 array and mounted it at /home so everything is saved.
You do the same thing by mounting your raid1 at /home/e-smith/files/ibays then every ibay would be on the mirror. Next, install another HD, and map it to something like /home/e-smith/files/users/temp and allow that user to be shared to everyone.
I am not a well versed person in Linux, but I think that would work.
HTH - Tom