@JJRdec Could you please open a new ticket with a description on how to reproduce the issue?

[JJRdec]

          @JJRdec Could you please open a new ticket with a description on how to reproduce the issue?

I just tested uploading a 1GB file:

truncate -s 1G output.file
aws s3 cp ./output.file s3://bucket-a/ --endpoint-url=http://localhost:9090

The upload itself is really fast, at least locally when running S3Mock and copying a 1GB file to a bucket, it uploads with 250MB/s.
AWS CLI is using a multipart upload automatically. What is taking a while is the process of merging all parts into one file during the completion of the multipart.

Please keep in mind that S3Mock is meant to be used for local integration testing.
Usually, small files are sufficient to test this.

Originally posted by @afranken in #1115 (comment)