What is the explanation of the following phenomenon observed in local file copy speed?
As you can see, it keeps stable at 120 MB/s, but at the beginning, it was nearly double of that.
Is there some kind of "bandwidth-shaping" in place?
In this specific case, the file is copied between folders on the same internal mSATA SSD drive.
I can consistently reproduce this, even with much higher initial speed:
The suggested duplicate answer indicates that initial speed bump could be caused by caching. But this seems unlikely as the sole reason because:
if it was only caching, the troughput decrease would be quite steep (after cached content got exhausted), but we are observing relatively slow and fluent decrease
if it was only caching, it could hardly cover initial 3 GB of transferred data until the speed settles down. 3 GB is too much for caching. Machine RAM is 8 GB, used is 6 GB, extra 1 GB is occupied during the entire copying process.
I can observe the same initial speed bump even with caching disabled:
Without caching, the average speed is consistently half of the speed seen with cache. This is the evidence that caching accelerates the entire copying process, so initial high speed must be attributed to something different.
So there must be something else. What it is?