The IN clause

R-tree indexes are stored in dbspaces. If you do not specify an IN clause when you create an R-tree index, the index is stored in the same dbspace or dbspaces as the table on which it is built and inherits the distribution scheme of the table.

You can store R-tree indexes in dbspaces that have a non-default page size.

You cannot store R-tree indexes in sbspaces. If you specify an sbspace in the IN clause of the CREATE INDEX statement, the index is stored in the same dbspace or dbspaces as the table.