The Lotus Notes 64GB database limit

One solution to this limitation is to use DAOS: Domino Attachment and Object Service:
http://www.ibm.com/developerworks/lotus/library/domino-green/

Another solution is to use Domino-DB2 Integration:
http://www.ibm.com/developerworks/lotus/library/domino-db2/

Or, create a new database where all attachments of the current database will moved to.
Then the rich text field of the original document will contain a document link to where the attachment has been moved to.

How to fix a database that has reached the 64gb limit:

1. Temporarily prevent replication
2. Purge views
3. Delete the database index
4. Create an archive database
5. Copy large documents to the archive database.
6. If possible, delete the copied documents from the database. 
• Sometimes this is not possible because document links that point to these large document will be broken. In this case, remove the contents of the document and replace it with a document link that points to the document you copied to your archive database.
7. Run Fixup on the database. We need this to ensure that we can compact the database.
8. Compact the database.
• If compact does not reduce the size of the database, try creating a new replica of the database. Then delete the old replica and replace it with a new replica
9. Re-create the index. 
10. Re-enable replication.
11. If the database has a replica that has also reached the 64GB limit, force a replication so that we get any update from that replica. Then delete that replica and create a new replica from our fixed replica.

More importantly, design your applications with scalability in mind!
Instead of performing a workaround by archiving large documents, a new database should be created, let's say: per quarter, per half year, or per year.