Using Synology for Back-ups
I tried setting up my new Synology as a Time Machine back-up. There are two 1 TB drives in 2 of 4 bays so plenty of room. Problem is the space I have allotted fills up and then when it is time for it to run a back-up again the time machine app says that it cannot because the disk is full. It is not taking off the oldest data to make room as happens in my Airport attached Time Machine disk. Does anyone know how to fix this behavior ?
Time Machine should act the same regardless of destination. That said, we've definitely seem Time Machine get gummed up and not be able to rotate out the old backups. You might need to delete your backup and start over.
Before doing that, though, it's worth going through this Synology KB article about setting up a Time Machine quota. The idea is you set up a different user account for each Time Machine Mac, and that way you can keep Time Machine from simply using all your available space.