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I use external SD cards to backup important data on my PC. I typically use "Robocopy /mir /ndl" so that I get on the SD card a true picture of what's on the disk.

Twice a year, when the clocks change, the copying process gets funny and starts copying the whole set of files, and on investigation it seems that the timestamps on the exFAT formatted SD card are one hour off.

This does not happen with NTFS.

Is this a bug with Windows 7 or some intrinsic flaw with exFAT ? It seems exFAT stores the GMT time regardless of daylight savings, or it seems that Windows reads the times without adjusting, as it does when it reads the times off of the NTFS partitions.

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NTFS is a 64 bit time stamp, ex fat uses 3 separate fields to store the time stamp with one byte being the time zone for UTC time.

I'd have to go back and look, but you can get details from the SANS paper or look around rshullic.wordpress.com

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This is probably a bug with Windows 7 (say, FileTime/SystemTime) or robocopy (timestamp comparison). Microsoft does not have the best record when it comes to not effing up UTC conversions (example). Maybe try it on a VirtualBox with pass-through USB running Windows 10 and see if it gets fixed? If it's not, open a ticket for MS and hope they read it.

You are right about the no-DST thing. Microsoft has released the exFAT spec somewhat recently, and the UtcOffset field is clearly stated to be simply an offset in 15-minute increments, not some "timezone location" string like America/Chicago that depends on the DST status. Could be a mistake from sharing code with FAT.

NTFS timestamps are always UTC.

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