When using Amazon S3 (Simple Storage Service), understanding how charges apply to data transfers can help you optimize costs and performance, especially when using advanced features like S3 Transfer Acceleration (S3TA) and multipart upload. This article breaks down the costs involved in using these features, and what happens if transfers fail.

1. Standard AWS S3 Data Transfer Costs

By default, AWS charges for data transferred in and out of S3 as follows:

• Data Transfer In (Uploads): Data transferred into S3 from the internet is generally free.
• Data Transfer Out (Downloads): When data is downloaded from S3 to the internet or other AWS regions, charges apply based on the amount of data and its destination. For example, downloading data to another AWS region incurs cross-region data transfer costs.
• Transfers Within a Region: Data transfers between services in the same AWS region (like from S3 to EC2 in the same region) are usually free.

If you frequently upload or download data over long distances or from unstable network conditions, S3 Transfer Acceleration can significantly improve the speed of these transfers, although it comes with additional costs.

2. AWS S3 Transfer Acceleration (S3TA) Costs

S3 Transfer Acceleration (S3TA) is a feature that speeds up data transfers by using Amazon CloudFront’s globally distributed edge locations to route data to and from S3 more quickly. This is particularly useful when you are uploading or downloading large files over long distances.

Here are the important things to know about S3TA charges:

• Uploads: When using S3TA, uploads to S3 incur additional costs beyond the standard data transfer rates. These extra charges are based on the volume of data transferred using S3TA.
• Downloads: Similarly, downloads using S3TA also incur additional fees.
• Cross-Region Transfers: If you are transferring data between S3 buckets in different AWS regions using S3TA, you will be charged both the S3TA fee and the cross-region transfer fee.

3. Multipart Upload: Handling Large File Transfers

For large files, AWS recommends using multipart upload, which allows you to upload a file in smaller parts rather than as a single, large object. This method improves upload reliability and performance by breaking the file into parts that can be uploaded in parallel or retried individually in case of failure.

Key points about multipart upload:

• No Extra Cost for Multipart Upload: AWS doesn’t charge additional fees specifically for using multipart upload. AWS charges you based on the total data you upload, just like regular uploads.
• Benefits of Multipart Upload: If a part of the file fails to upload, you only need to retry that specific part, instead of restarting the entire file upload. This feature is crucial when uploading large files with unstable network conditions.

4. Combining Multipart Upload with S3 Transfer Acceleration

When you combine multipart upload with S3 Transfer Acceleration, you get both the performance benefits of breaking files into smaller parts and the acceleration of transfers through CloudFront edge locations. However, keep in mind the following:

• Charges for Each Part: Each part of the multipart upload that uses S3TA is charged for S3 Transfer Acceleration. If a part of the upload fails and doesn’t complete, you won’t be charged for that specific part.
• Retry Failed Parts: If a part of the multipart upload fails, you can retry uploading that specific part without affecting the rest of the transfer. This is more efficient than restarting the entire upload.
• Storage of Uploaded Parts: S3 stores the parts of a multipart upload as they are uploaded. If an upload fails and is never completed, AWS will still charge for storing the uploaded parts. To avoid unnecessary storage costs, set up lifecycle rules that automatically remove incomplete multipart uploads after a specified time.

5. What Happens When Uploads Fail?

When an S3 transfer fails, the cost implications depend on whether you’re using multipart upload or not:

A. With Multipart Upload:

• No Data Transfer Charges for Failed Parts: AWS only charges for successfully transferred parts. If parts of a multipart upload fail, you won’t be charged for them.
• Storage Costs for Incomplete Uploads: If some parts were successfully uploaded before the failure, AWS will charge for storing those parts. Use the AbortIncompleteMultipartUpload feature to automatically clean up unused parts after a certain period.
• Retry Failed Parts: You can retry uploading just the failed parts, which saves time and bandwidth compared to restarting the entire file upload.

B. Without Multipart Upload:

• Retry the Entire Upload: If you’re not using multipart upload and the transfer fails, you’ll need to retry the entire upload from scratch. For large files, this can be time-consuming and inefficient.
• No Storage or Partial Charges: Since no parts are stored during a failed upload, you won’t incur storage costs for incomplete uploads. However, if some data was successfully uploaded before the failure, you will be charged for that data transfer.

6. Why Multipart Upload is Preferred for Large Files

Using multipart upload is strongly recommended for large files because:

• Efficiency: Multipart uploads allow you to upload large files in smaller parts, making it easier to handle failures and ensuring that each part is uploaded successfully.
• Avoiding Full Retries: If a file upload fails with multipart upload, you can retry only the failed parts, rather than starting over. This saves time, bandwidth, and money, especially for large file transfers.
• S3TA Compatibility: Multipart uploads work seamlessly with S3 Transfer Acceleration, allowing you to benefit from faster uploads, even for large files, while minimizing the risk of failures.

Conclusion

AWS S3 offers a range of features to optimize file transfers, such as S3 Transfer Acceleration and multipart upload. Each feature comes with specific benefits and cost implications:

• S3TA improves transfer speeds at an additional cost, making it ideal for long-distance uploads.
• Multipart upload enhances reliability and efficiency, especially for large files, and helps avoid full retries in case of failure.

In cases of failure, both features ensure you are only charged for successfully transferred data, but it’s important to manage incomplete uploads to avoid storage charges. Combining these features can greatly improve both speed and reliability for transferring large amounts of data to and from AWS S3.