difference beetwin hd Seagate SAS ST3450856SS and ST3450857SS

[geotropa]

Do you know the difference beetwin hd Seagate SAS ST3450856SS and ST3450857SS ? It's possible to install in raid5 with n.3 HD ST3450856SS only n.1 new HD ST3450857SS ?

 

[popatim]

The only difference seems to be firmware related. The drives should work fine with each other in raid.