I read the documentation from the official website. but it does not give me a clear picture.
Why would need to use AWS Transfer Family since AWS DataSync can also achieve the same result?
I notice the protocol differences, but am not quite sure about the data migration use case.
Why would we pick one over the other?
Why would need to use AWS Transfer Family since AWS DataSync can also achieve the same result?
It depends on what you mean by achieving the same result.
If it is transferring data to & from AWS then - yes both achieve the same result.
However, the main difference is that AWS Transfer Family is practically an always-on server endpoint enabled for SFTP, FTPS, and/or FTP.
If you need to maintain compatibility for current users and applications that use SFTP, FTPS, and/or FTP then using AWS Transfer Family is a must as that ensures the contract is not broken and that you can continue to use them without any modifications. Existing transfer workflows for your end-users are preserved & existing client-side configurations are maintained.
On the other hand, AWS DataSync is ideal for transferring data between on-premises & AWS or between AWS storage services. A few use-cases that AWS suggests are migrating active data to AWS, archiving data to free up on-premises storage capacity, replicating data to AWS for business continuity, or transferring data to the cloud for analysis and processing.
At the core, both can be used to transfer data to & from AWS but serve different business purposes.
Your exact question in the AWS DataSync FAQs:
Q: When do I use AWS DataSync and when do I use AWS Transfer Family?
A: If you currently use SFTP to exchange data with third parties, AWS Transfer Family provides a fully managed SFTP, FTPS, and FTP transfer directly into and out of Amazon S3, while reducing your operational burden.
If you want an accelerated and automated data transfer between NFS servers, SMB file shares, self-managed object storage, AWS Snowcone, Amazon S3, Amazon EFS, and Amazon FSx for Windows File Server, you can use AWS DataSync. DataSync is ideal for customers who need online migrations for active data sets, timely transfers for continuously generated data, or replication for business continuity.
Also see: AWS Transfer Family FAQs - Q: Why should I use the AWS Transfer Family?