In article ,
says...

In article , ham789
@netzero.net says...

On 5/20/2018 7:58 PM, Jason wrote:
This has been discussed quite a lot before, but it
continues to interest me. I create a full image backup of
my system once a week and an incremental backup each of
the next six days. Backups (Acronis) go on a spare HD
partition and I then copy them to an external (WD)
Passport 2GB drive. Copying the full backup image takes
over an hour. What I've noticed, usually, but not every
time (!?) is that the transfer gradually slows down. See:
https://imgur.com/hESFJq1

While the copy proceeds there is no other activity beyond
the usual Windows background stuff running - no apps,
browsers, etc.

What might account for this?

I've seen odd slowdowns using file manager.
Same copy using totalcommander doesn't have that problem.

How fast is your external drive?
I'm assuming you meant 2TB??
When I copy to external media, it starts fast, but then drops
to a much lower speed somewhere around the 1GB transferred point.
Pausing for a while restores the speed.
I'm theorizing that the fast speed is how fast the internal drive
can write to a buffer. The slow speed is the speed that the external
drive can accept the data.
This is exceptionally obnoxious with 256GB USB thumb drives.

Opps. Yes, TB not GB.
It's a USB3 drive. When things are clipping along the copy
proceeds at 100MB/s +/- a little. I see the slowdown start
very early into the transfer. The graph shown is of a 450+
GB transfer. I haven't tried pausing it and re-starting.
I'll see if that has an effect.

Don't those things use some type of buffer? I'd assume once buffer is
full and keeps being filled the actual writing would slow down. Small
file and buffer doesn't get filled, large file and it's continually
being filled.