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Question: Time Machine 2e disk Issue, High Sierra 10.13.1 ...

I am using a second external disk(B) to make a second Time Machine backup of my 1Tb+ space residing on internal 1Tb iMac Fusion disk(X) and an external Lacie 3Tb Thunderbolt2(Y). Alternatively it uses the one(B) then the other disk(A) to backup; perfect! But since High Sierra, after a number of successful incremental backups on both disks(A) and (B), the second one (B) backs up the total 1Tb+ space(X)+(Y), to be backed up, a second time without anything fundamentally changed and so using up all space on the second BU disk(B). I stopped that process and re-initialised disk(B) thoroughly and re-started the process with adding the empty(B) again to Time Machine. After a few successful double incremental backups on (A) and (B) the problem resurfaces and the total space is being back-up two times on the second backup disk(B) without a reason that I can see, while (A) stays normal taking incremental BU's. The situation is troubling my confidence in Time Machine as my important backup basis!

Anyone experiencing the same or having a solution to this?

Thanks in advance!

Using iMac27inch macOS 10.13.1, (A): Lacie 6Tb Thunderbolt2, (B): WD MyBook 2Tb

iMac (27-inch, Late 2012), OS X Mountain Lion (10.8.5), null

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Nov 12, 2017 9:14 AM in response to polimo In response to polimo

Correction: also on BU disk (A) large numbers of Gb's(800Gb's) are being re-backed up in the incremental, although nothing has changed in the data...

Nov 12, 2017 9:14 AM

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Nov 14, 2017 12:30 PM in response to polimo In response to polimo

Addition.... it looks as if large portions of the data(800Gb+) from (X) and (Y) are being re-backed-up as a whole regularly to both BU drives (A) and (B) without data has been changed; so filling up BU disk space very fast.

Nov 14, 2017 12:30 PM

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Question: Time Machine 2e disk Issue, High Sierra 10.13.1 ...