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Why does Time Machine seem to be doing a complete backup (18-20 hours it says at various points!!) when I previously did the first backup on this drive? (About 650 GB of data.) I've done packups on different backup drives, and haven't done this in a few months. But it seemed to recognize the drive and began backing up as soon as the drive came up.
MacBook Pro 13", OS X 10.11
No. There is no reason to suspect that, although some things can occur that cause TM to conclude its existing backup is of another Mac.
A trivial example would be if you changed the name of the Mac's startup disk. In that case TM would consider the newly named disk to be a different one entirely. That really would be a brand new backup (and TM will let you know).
Under normal circumstances, if ten or more days elapsed since the last backup TM will exhaustively compare the contents of the source and backup disks to determine what needs to be backed up and what doesn't. The longer that period of time, the more files are likely to require backup. The resulting time and data estimates can be wildly inaccurate.
No. There is no reason to suspect that, although some things can occur that cause TM to conclude its existing backup is of another Mac.
A trivial example would be if you changed the name of the Mac's startup disk. In that case TM would consider the newly named disk to be a different one entirely. That really would be a brand new backup (and TM will let you know).
Under normal circumstances, if ten or more days elapsed since the last backup TM will exhaustively compare the contents of the source and backup disks to determine what needs to be backed up and what doesn't. The longer that period of time, the more files are likely to require backup. The resulting time and data estimates can be wildly inaccurate.
If TM has not backed up to that drive in several months, it's probably normal.
Thanks.
Does that mean it starts from scratch rather than doing an incremental backup?
Thanks. Very helpful.
Second Time Machine Backup Problem
