When you are adding 10 to 20 percent or more to a large table, drop the nonclustered indexes, load the data, and then re-create nonclustered indexes.
For very large tables, you may need to leave the clustered index in place due to space constraints. Adaptive Server must make a copy of the table when it creates a clustered index. In many cases, once tables become very large, the time required to perform a slow bulk copy with the index in place is less than the time to perform a fast bulk copy and re-create the clustered index.
