Expandable rack mount system.

I am looking to create the following set-up and was just wondering whether or not it would be actually possible.

I can see it working in my head but dont know if the ardware actually exists because I'm not as up to snuff on rack mount stuff as I am on regular cases.

1 U Rackmount server running Linux on mirrored drives.

Multi U chassis storing multiple hard disks for data back up, each drive beonging to a seperate client or group for back-up purposes. As more clients come on board we simply add another drive just for them, when the unit is full we simply add another unit. The drives are hot swappable/removeable so that if required we can take the drive out and deliver it to site to restore their systems immediately or we can restore via the web if more appropriate.