copy /u and timestamps

Oct 18, 2008
305
1
Hello — what happens with commands like copy /s /u ... ( and move /s /u ) when the file system for the source and target are not then same? In my case, the source is ntfs (well the source is mapped drive from my personal NAS which is running some version of samba) and the target is exFat? I think the that (file) timestamp for exfat is a 32 bit value and ntfs is a 64 bit value to the sub-second. So unless I use the /uf option can the copy/move be skew? Thanks
 
May 20, 2008
10,671
83
Syracuse, NY, USA
According to the help,

/UFCopy each source file only if it is more than 2 seconds newer than a matching destination file or if a matching destination file does not exist (see also /CF and /U). Do not use /UF with @file lists.

exFAT only knows times to 2-second granularity. The exFAT timestamp has 5 bits devoted to seconds. That's only 32 values so it's interpreted like this:

timestamp 0 = 0 seconds after the minute
timestamp 1 = 2 seconds after the minute
timestamp 2 = 4 seconds ...
...
timestamp 29 = 58 seconds ...
timestamp 30,31 unused.
 
May 20, 2008
10,671
83
Syracuse, NY, USA
I have read that even though exFAT uses the DOS date/time format (with 2 second resolution) it can do better. It has another BYTE whose value is a number of 10ms intervals (0 to 199) after the even-second mark (now it can do times to 10ms) and another BYTE to indicate time zone offset (so, in effect, it can do UTC times to 10ms). I think OSs in general mays or may not take advantage of those features.
 
Oct 18, 2008
305
1
Yes --- I found that too -- it seems that MS did publish the specs on exfat, but its not clear what OS'es are using that option order even the timezone field -- I guess since it seems that SDXC cards drove this we can see how the camera makers take advantage of all this -- thanks again for into