Upload Speed to S3 limited to max 10 MB/s

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?

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.

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

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

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

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

Sure.

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 is not complete, so I cannot tell)

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

Using WinSCP 6.5, when starting an S3 Upload or Download, speed is limited to 10MB/s

When "touching" the speed limitation button, to change from "unlimited" to "unlimited" (yeh.. the same...just to confirm you want max...) THEN, the speed limitation disappears...

so it's just a "default speed is wrong"......

I also have this issue. WinSCP v6.5.7. Not Amazon S3, but S3 compatible with SeaweedFS v4.48.

Cyberduck maxes out my wireless connection at ~115 MB/s. WinSCP maxes out at ~18 MB/s. Disabling or enabling "Optimize connection buffer size" makes no different. Changing the speed from "Unlimited" to "Unlimited" also makes no different.

Additional testing on Linux machine with awscli, same system but from a VM this time.

s3.max_concurrent_requests 10 (default): ~100 MiB/s -> ~105 MB/s
s3.max_concurrent_requests 1: ~49 MiB/s -> ~51 MB/s

So I have no idea what WinSCP is doing. Too bad. I like this tool for my file transfer needs.

@Vuhuy: Thanks for your report.

Can you send me an email, so I can send you back a debug version of WinSCP to track the problem? Please include a link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.