You can put all the tablespaces in the backup state at the same time no matter if you use RAID, EMC, single disk, SAN or any other disk configuration. But no matter how your thisk are configured, this is not realy a very clever thing to do. The recomended way is to put a single tablespace in backup mode, backup its datafiles, put TS back into normal mode and proceed to the next tablespace untill you back up all the tablespaces.