Two thoughts: first, is each Time Machine drive trying to back up the full 1 TB internal drive and not just the one partition?
Second, are the TM drives empty or do they contain the previous backups? Since the partitions are "new drives", TM should want to back up everything fresh and for the first time, requiring more space. Otherwise…?
On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
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