Slow initial Chkdsk /R on new 18TB WD Elements

Why is the //Windows 7 64//Chkdsk /R// sector-by-sector-verify performance
on WD Elements 18TB external USB drive so slow ?
Who else has tried Chkdsk /R on this WD 18TB external USB hdd hard drive ?

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Chkdsk /R on new and empty WD Elements 18TB is now at 72% ,
after 235 hours (almost 10 days) .
72 percent complete. (1517398666 of 2197240073 free clusters processed)

I have just started a chkdsk /r on my 18 TB WD elements and it appears to be headed in the same direction. It has been running now for about 28 hours and the ETA is increasing more quickly than the seconds are passing even though it seems to be running at a good bit over 1KB/sec.

I ran it because I moved a large folder (several TB) onto it from another drive that was getting full. After the move was complete the folder was there and appeared intact, but after I powered down for the night and rebooted the next morning it was just gone without a trace! I’m doing this basically as a Hail Mary in hopes of getting my folder and its contents back, and some of the results from the earlier passes (which completed after about seven hours) indicate that I may have some hope, but I cannot tell whether or not this is true because the drive is inaccessible while the chkdsk utility is running. I am now up to 7% “looking for bad free clusters,” 34% total completed, and at the rate it is progressing it could well take two weeks or more to complete.