1. By analyzing command of sp_spaceused, we found that table tAlarmToTrail occupied too much space in TNSDHDB, but in fact, the real data in tAlarmToTrail was very little.
2. By more analysis and tests, we found that when we repeatedly deleted and inserted data to tAlarmToTrail, which caused that the spaceoccupied by tAlarmToTrail increased continually.
3. Finally, we were sure that the reason is from bug of Sybase, but SQL Server has no such bug.
4. Defragmentation can solve this problem normally, and sometimes database expansion is necessary.