You'll need carriers/caddies with adapters for the smaller drives: [URL] 
Looking for suggestions, experience and a BOM to Convert my (4 year old) 4 bay R310 Server currently fitted w/ 2 x 1TB 7.2K RPM SATA 3.5in to 4 x 500 GB 2.5in. TIA B
Convert R310 Server w/ 2 x 1TB 7.2K RPM SATA 3.5in to 4 x 500 GB 2.5in