Among other things, SMS stands for "System Managed tableSpace" in an IBM DB2 database. With an SMS tablespace, the operating system manages allocation and deallocation of physical storage as needed to accomodate database data. An advantage to SMS is the ease of administration - because the OS handles everything automatically, the database administrator can focus on other tasks. This price for this convenience is paid in performance, since there is overhead and inefficiency involved in making high-level calls to the OS rather than doing the low-level file work manually. The alternative, DMS, offers greater performance and flexibility, but requires constant monitoring and maintenance attention to keep things running smoothly.