When I tried to do do a TM backup to my external HD TM doesn.t see my existing backups and tries to do a new complete backup. It first says "preparing backup..." which takes a long time before it starting making a new full backup not using the existing one to do an incremental one.
iMac, OS X El Capitan (10.11.5), 8 GB 1867 MHz DDR3
I have a 2TB iMac with a 2TB Time Capsule. The iMac has ~40GB free, while the TC says 1.93TB full. Is there a reason it stopped backing up? I assume that when it says "not enough room," it's trying to create a new back up. Is it possible to just run out of back up space for the TC with a similar sized HD on the iMac?
You are discussing two different things above:
You seem to be assuming that because Time Machine appears to be creating a new full backup, it therefore must not recognize the existence of any previous backups. This assumption is false. New full backups are created, for example, when updating OS X.
The way to check whether Time Machine recognizes previous backups would be to use the Time Machine application to check whether you can see previous versions of any files.
I did a search and came up with this site, http://pondini.org/TM/Home.html, which has a wealth of Time Machine information and trouble shooting. One thing they suggested was restarting the computer and after I did that TM recognized the existing backup and proceeded to update that one. Problem solved.
Time machine doesn't see existing backups
