You can backup and transfer your site while it's in use. However, for the sake of your sanity, I do recommend setting it to Offline mode in Global Configuration. The reason is that once you transfer your site you'll need to switch the DNS to the new server. Depending on how your DNS is currently set up it may take anywhere from seconds to two days. You don't want people using the old site during that time.
If you want your site transfer to go more smoothly I recommend that you set your DNS' TTL (time to live) to 300 seconds at least 3 days prior to moving your site. This means that once you switch the DNS over to the new host it will only take up to 5 minutes to see the new site and continue the restoration. This will reduce your site's downtime considerably.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
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