1.6TB Data - Sharp Decline in file copying speeds between USB drives

[ralphy]

I think you're seeing the effects of drive head seek latency when copying. Also, your drive will likely use its cache for smaller amount of data until it is finally written to the drive. This gives the impression that transfers are faster at the beginning as you have pointe out. As the cache fills up and the head seek latency increases depending on the number of files, their sizes and the final destination on the drive, you'll certainly see exactly what you described.


Alternatively, you can try rsync to monitor your transfer speed. For example:

Code:

rsync -PSauv sourcedirectory/* /dev/sdXX/destdirectory/

If you actually see a drop in transfer speed, as opposed to files that are just big in size, then your disk is I/O-bound hence more noticeable slow downs (often seen when writing heavily to a flash drive or an external USB device).