To choose the right strategy the migration of the site to another server, you first need to decide whether otlozhenie of writes/updates to the database during the transfer of the resource, i.e. the actual simple? Suppose that we started the transfer of the loaded online store, where every three minutes the order. If you stupidly remove the database dump, make an archive of files, overtake on another server, deploy the whole thing, the lag time will be a minimum of 30 minutes, even if that new piece of hardware will be in the same rack. While there will be a migration, the old database will already recorded new orders. As a variant it is possible during migration to prevent the creation of orders and users, but a simple 30 minutes (actually 2 hours) is not satisfied, so on large projects practiced a seamless move - first, install the balancer, it is overwritten DNS, and he, in turn, proxies the traffic to the old server, then raised a second server, it unfolds the database, which poluchaetsya to the database on the old server as slave, the sync scripts rsync/csync, the files are submitted to the cloud. Finally, we obtain the classic master-slave model. In conclusion, changing the roles in the database, make a new master and old slave. Simmer the old server.