Many thanks for the detailed response! 
I will play around with the options you suggested ( --checksum, --s3-upload-cutoff)
Are the 10 million files in one directory or are they in a folder structure? If they are in a folder structure about how many files per folder are there?
They are on a single minio bucket (ie, one directory).
How big are the files you are copying? You might want to raise
--s3-upload-cutoffso that they are all copied in a single transaction. This will ensure they have an md5sum and is likely to be more efficient for medium size files (say < 1 GB)If you are uploading large files then tweaking --s3-concurrency and --s3-chunk-size can make a difference at the cost of using more memory.
The files are pretty small, ranging from 100 bytes to 1Mb max.
Do existing files get updated? Or is it write once, then delete? There is a workflow which will work for that...
These are Kafka messages and hence it's written once and they won't get updated/modified, Do we have any specific options those are well suited for this scenario? Thank you!