How to estimate the time needed for transferring files between internal and external drives?

Question

My laptop usb port is usb 2.0. my external hard drive is usb 3.0. Wikipedia says

Due to bus access constraints, the effective throughput of the High Speed signaling rate is limited to 35 MB/s or 280 Mbit/s.

The total size of the files I need to transfer is 17GB.

1. How can we estimate the time for file transfer? Simple calculation shows that the time for transfer is

   17*2^10/35/60 = 8.3 min.

2. I use rsync to perform the transfer under Ubuntu, and I also time the transfer:

   $ time rsync -a /media/t/2/  ./   
   real    106m45.245s
   user    3m6.938s
   sys     1m25.902s
   

   Note that I also do two other similar rsync data transfer between the same internal and external hard drives at the same time. All other programs are not active, but I guess data transfer between the hard drives don't take much cpu time (sys + user).

   Still the difference is big (106min vs 8.3min). what factors contribute to the time mainly?

Thanks!

Answer 1

Several additional things to consider here.

• Number of files. Transferring a single large file and many files differs greatly. This is due to the added operations and latency of reading and writing each file.
• performance of both disks involved, seek time, spindle speed, etc.

To arrive at a solid calculation is difficult as there are many variables at play. If you want to see where the biggest bottleneck is you should look at performance testing each step in the chain. Mainly I would focus on a perf test of both internal and external disks as a USB2 interface will likely be slower than either. ATTO is a good starting place ATTO Benchmark