I’m currently watching the progress of a 4tB rsync file transfer, and i’m curious why the speeds are less than the theoretical read/write maximum speeds of the drives involved with the transfer. I know there’s a lot that can effect transfer speeds, so I guess i’m not asking why my transfer itself isn’t going faster. I’m more just curious what the bottlenecks could be typically?

Assuming a file transfer between 2 physical drives, and:

  • Both drives are internal SATA III drives with 5.0GB/s 5.0Gb/s read/write 210Mb/s (this was the mistake: I was reading the sata III protocol speed as the disk speed)
  • files are being transferred using a simple rsync command
  • there are no other processes running

What would be the likely bottlenecks? Could the motherboard/processor likely limit the speed? The available memory? Or the file structure of the files themselves (whether they are fragmented on the volumes or not)?