Running a 2009 iMac on 10.11.6. I had turned off TM a couple weeks ago while I did some updating. I turned it back on yesterday, clicked backup now, and when I returned to check on things several hours later, TM had blown away all my backups and done one entire new backup instead of updating. The TM drive is a 1 TB connected via USB. I use the FW connection for a 2nd clone backup. Current system is 541GB. A. Why did TM blow away weeks ( months ?) of backups when turned back on ? Why did it not just update with changes since the most recent backup ? B. With the one backup it did yesterday on the drive, it now says "there isn't enough space on TM drive"- backup failed. Why did it hum along happily for months with the system the same size using the exact same external drive ? Why isn't it just updating the backup done yesterday ? The loss of the TM backups is distressing as I was going to pull a few things from an older one. How do I move forward and prevent this from occurring again ? Thanks for any help.