Time Machine resets when External HD is disconnected and reconnected.

[ChrisDev]

I had set up Time Machine to backup my MacBook Air on an external HD. It was doing this just fine for a week. I had a week of backed up data, but just yesterday I safely ejected the HD and, today, reconnected it. But now there is only backup data for today and does not go back any further. As if it never backed up the past week's data.

Are there steps I need to take if I want to disconnect an external TM HD?

 

[IowaLynn]

In case the drive is failing... an alternate and a2nd backup method.
Try repair in DU can be lengthy.
how much free space on it?
How much data is being backed up?

 

[ChrisDev]

It's a 500GB partition of the HD.
320 GB is available.