DT3 is quit on my Mini
Why?
but when I open the MBAir, none of my databases show as open and when I try to open them, I get a popup telling me that that database is either in use or has not been closed properly.
This behavior has nothing to do with sync or the Mac Mini. You aren’t opening databases on the Mini while on the Air. Each device has its own copy of the database(s).
In order to sync should DT be open on both computers?
Yes, logically as one device is acting as the server, the other the client. This is just like making a phone call. If no on is awake to answer the phone, you call isn’t answered.
I thought sync was kind of an automatic process.
You need to define “automatic”. As has been discussed many times, sync is optional and it’s up to you to decide what syncs and to what devices. Our software doesn’t and won’t just sync of its own volition. So making a new database will not magically make it appear on your other devices.
Did you read this forum post…
By the way, I’d recommend giving this a read: Help > Tutorials > Understanding Sync…