2. Data conversion – Just because your installation of FreeBSD ran a MySQL server does not mean your new CentOS server will handle your databases exactly the same way. Make backups and test all data conversion before you go live.
3. Learn the server – A new operating system means a new system for you to learn. Even switching from one Linux distribution to another may present some differences with package management systems and configuration file locations
4. Consider the money – After you have assessed all of the technical ramifications of migration, you need to quantify them. How much will it cost to actually make the change? The cost of the new server and OS are only a small part of the total amount involved in the migration.