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/s5.0Gb/s read/write210Mb/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)?
Haha and now you know exactly WHY they do that! The manufacturers were more than happy to let people keep believing SATA3 drives would be faster than SATA2 drives until they started facing public backlash and the costs of returns, but they still try to bury it in the fine print.
Keep in mind that any transfer speeds on the box are also going to be best-case scenarios, for read access only (because writing takes longer than reading even on an SSD). The numbers I found on reviews are generally going to be more real-world conditions including a combination of simultaneous read/write operations. Personally I don’t trust anything except what I can get in my own installations because everyone’s hardware and software are different, but if you decide to do your own testing make sure that it disables cached operations during the tests or you’re not doing anything but checking the speed of your RAM.