When you are adding 10 – 20 percent or more to a large table, drop the nonclustered indexes, load the data, and then recreate 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 amount of time it takes to perform a fast bulk-copy and recreate the clustered index.
