reservepagegap and sorted_data options to create index

When you create a clustered index on a table that is already stored on the data pages in index key order, the sorted_data option suppresses the step of copying the data pages in key order for unpartitioned tables. The reservepagegap option can be specified in create clustered index commands, to leave empty pages on the extents used by the table, leaving room for later expansion. There are rules that determine which option takes effect. You cannot use sp_chgattribute to change the reservepagegap value and get the benefits of both of these options.

If you specify both with create clustered index: