Thanks. Where are you uploading the files exactly to? Is that AWS? Or some other storage implementing S3? (as it's not an AWS hostname)

Are you using the latest version of WinSCP? (the log it not complete, so I cannot tell)

Can you try to disable "Optimize connection buffer size"? https://winscp.net/eng/docs/ui_login_connection

Sure.

@rokj: Please post some screenshots documenting the upload speed in WinSCP and Cyberduck. Log files might be useful too.

Yes, we tried Minio client and Cyberduck and on both throughput goes to the maximum upload available.

@rokj: Do you get better throughput with any other S3 client running on the same machines as WinSCP?

We still have the same problem. We are using WinSCP version 5.21.1

We didn't optimize our S3 implementation for speed yet.

This issue is tracked already:
Issue 1732 – Improve S3 transfer speed
You can vote for it there.

Hi,
I am using WinSCP quite often to access different AWS S3 buckets which works very well and is easy to automate with the configuration file.
Now I have a use case where a user need to upload up to 5 TB of data. I noticed that the upload to S3 is normally between 7-8 MB/s. Sometimes its shortly up to 10 MB/s but not more. I have a 1 GBit/s internet connection so I assumed to get at least 70-80 MB/s in upload speed.

When I upload the files directly from aws cli it works like expected so my guess is that there is a bug/limit/whatever in WinSCP. Anyone can help me here? Perhpas there are some hidden configurations?