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#11
My 2 x 4TB WDC USB 3 drives came formatted as exFAT, noted on the package as usable with PC and Macintosh [Mac OS X had issues writing to NTFS but could read it]. I connected them and reformatted as NTFS before putting data on them, my MacBook Pro had died earlier. I don't think the formatting can be changed without losing the data on them but since yours are used as backup storage that wouldn't be bad, just reformat the exFAT to NTFS and create a new backup. Linux can work with either format and several more.