Without going into mind-numbing detail, I'm trying to back up the external drive I'm right now booting from. It has about 900GB of data and runs Mavericks.
The external is now the only source of my data in an OS other than El Capitan and I need to back it up.
I also have another 900 GB on the internal, which runs El Capitan and won't boot. I'm downgrading to Yosemite so all this data will be zapped once the restore happens. I have a Yosemite installer on a thumb drive.
Time Machine is backing up both, about 1.8 TB.
If I reformat the internal, will Time Machine recognize it has no data and just move on to backing up the external?
Thanks.