Once in every 6 months but you can get in problems with your home country eventually if they see you going like that on a UAE residency visa. Asian countries like India, etc are also looking into this now. Don't abuse the system or you will be looked at thoroughly soon. Good luck. It is due to all this EU and OECD are blackmailing countries like UAE, Panama etc.How many days in a year you need to live in UAE in order to maintain your visa valid and renewable the next year?