Data archivation - UNION from two hosts

I have stats in 4-node cluster and database now have about 2.4TB. I want to make "archive server" and move old data from cluster. My idea is on cluster create FEDERATED table from archive and if someone query old data (minimum requests), then make UNION between live and FEDERATED table. My question - is this good solution, or can someone recommend better solution?

For better understand of database - it's analytics app, every user have own table and most of queries are on last two months data. About 300 php scripts working with stats, so I try to find easiest way how to implement archivation with minimal app rewriting.