I was curious and had a 128GB Lexar Flash Drive sitting around from a failed experiment and found
  • if the flash drive were formatted Mac OS Extended (HFS+) with a GUID partition table I could remove it from the Time Machine exclusion list.
  • the same flash drive formatted ExFAT with a Master Boot Record partition table could NOT be removed from the Time Machine exclusion list.
Since MBR and ExFAT are the de-facto standards for high capacity thumb drives and SD cards and my results verified what you are seeing, I didn't attempt to test all the possible permutations of partition maps and format options, but I would venture the key is whether or not the drive is formatted Mac OS Extended. Given Time Machine's reliance, or should I say dependence, on the HFS+ volume structures that would not be surprising.

In the name of full disclosure, I should have said I am running Yosemite (OS X 10.10.2) on a Late 2012 Mac mini (Macmini6,2).

Last edited by joemikeb; 02/09/15 03:34 PM. Reason: add configuration data
If we knew what it was we were doing, it wouldn't be called research, would it?

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