3 years of backup disappeared on Time Machine

Hello,

90GB free isn't enough for Time Machine backups, and a drive from 2016 could be getting close to failure. I recommend you unplug this Time Machine drive and archive it, then start new Time Machine backups with a new external disk that is 2-3 times larger than the disks you're backing up.

These specific external hard disks, sold by Apple, are excellent options and compatible with Time Machine:

• LaCie 2TB Mobile Drive External Hard Drive USB-C - Apple
• LaCie 2TB Rugged USB-C Portable Hard Drive - Apple

If you have an iMac earlier than 2017, you will also need a USB-C to USB-A 3.1 cable, such as this one, for compatibility with your older generation Mac.

You can then Back up your Mac with Time Machine - Apple Support.

Jack

I forgot to mention, it is normally recommended a Time Machine drive be 2 to 3 times the size of the internal drive. So unless your Mac has a 512GB drive or less, a 1TB backup drive would be considered too small.

I can’t help with getting your old files back. However it should be noted that Time Machine is designed to do hourly backups which are useful when you’ve lost a recent file or you need to restore a new installation to the latest stable status. It was never intended for long term storage of archived files. With the lowering cost of storage, important files can be selectively stored on external drives.

But there is a way to recover the missing backups?

Unfortunately no.

FWIW, Time Machine was never meant to be an archival system. As far as what is a full disk. it would be "full" when there is not enough space to complete the current backup.

FWIW, there hasn't been an alert when Time Machine is about to erase something in the 15 years it's been available.

Actually if your Time Machine backup drive is working correctly after all of these years, then those old files should be condensed into the earliest backup that is showing.