Depending upon what you are doing you could partition the table(s) are perform a Merge Split.

http://blogs.msdn.com/b/felixmar/archive/2011/02/14/partitioning-amp-archiving-tables-in-sql-server-part-1-the-basics.aspx

http://blogs.msdn.com/b/felixmar/archive/2011/08/29/partitioning-amp-archiving-tables-in-sql-server-part-2-split-merge-and-switch-partitions.aspx

If not you will have to create some Tables and Stored Procedure.

I did this a few times but unfortunately I was not able to retain the code.

I wrote a script to create the Archive the Database. Create Logins, Users and permissions.

I wrapped the Archive (Select from the source to the Archive Database) into a Transaction.

I created a control table where I stored the batch size so that I could process a certain number of records at a time.

I also had a column that indicated the Total Number of Records to Process.

I also had a column to store a boolean value (Active_Inactive) so that I could determined whether to terminate the program before it processed the next batch.

I create a Stored that had a While Loop and it each time it would check the Active Column as well as the batch size (in the event that you decided to change the batch size).

I also created a log table so that I could track what occurred and when, etc.

I also had to create a view because the users wanted to include the archived Data in their Queries.

I have to agree that 20GB is not that much Data. So consider that before you embark on this.

I hope this helps.