Calculating transfer speeds - what am I doing wrong?

No idea what, but most likely I am doing something wrong in my calculation...

I am copying from one SSD to another SSD:
an entire folder with 45,0 GB
44708 files (1051 folders)
Opus shows a speed of 400+ MB/s which, I believe, is fair
With a stopwatch I measured 5 min 2 sec = 302 sec = 153MB/s avg.
However... Opus shows some 400MB/s avg.


oh BTW I noticed this when comparing TeraCopy with Opus.


It's the speed data is written, while data is being transferred. Copying files involves more than just transferring data, especially if lots of small files are involved. Each file has to be created, have its timestamps set, metadata copied, security updated, etc. according to what is configured in Preferences. That isn't counted in the speed calculation as it's usually a fixed amount per file and not indicative of the speed the devices are working at, which is what people are usually interested in.

Probably it has something to do with the small avg. size of the files.

Background of the above: I had to copy a -lot- of mostly large files from one USB drive to another yesterday.
As I expected this to take a lot of time, I checked out TeraCopy hoping it might speed up things a bit. So is also the chance to do some testing, i.e. checking whether or not it would indeed make a significant difference. I copied files using this tool and also using Opus. Copying from USB->USB (both using USB 3.1) obviously can not be compared with HDD copying SSD matters.

FWIW below my findings.

A table of numbers is not very helpful on its own.

Comparing file copy speed is really complicated, and almost always a large waste of both your time and ours when it comes up on the forum. Unless there's something wrong with a device somewhere (e.g. some do not like certain buffer sizes), the speed will be the same in almost all programs as it is limited by the hardware and the software spends almost all of its time simply waiting for the hardware to process read/write requests.

The exceptions are often down to how much extra work the programs do on each file; for example, some do not preserve timestamps, file attributes, NTFS metadata, permissions, and so on (all of which are configurable in Opus). Or down to buffering (if you copy data in one program, then another, it may already be cached and not have to be read again). There are other factors and complications as well.

There's already a thread elsewhere on the forum comparing TeraCopy and Opus for speed and the majority of people who participated in it say the speeds are the same. One or two found one program or the other slightly faster, probably due to random factors of their hardware.

Occasionally a thread like this reveals a pathological case in Opus. For example, it was recently found that updating the progress dialog with a huge number of tiny files could slow things down a bit, and we addressed that in an update. But unless you have something concrete to show us and understand how to test copy speed, including buffering, and ensuring both programs are doing the same thing, then it's not something I want to get into as we have a thread like this every six months or so and 9 times out of 10 it's a waste of time that just ends up with us explaining proper testing methodology; time which could be spend improving the program instead.