A development EC2 instance is uploading 500,000 files of 1 GB each to an S3 bucket in the same Region with default encryption. Application logs show it is frequently waiting for writes to S3; network bandwidth is not the bottleneck. What change should improve S3 upload throughput?

Distributing write operations across multiple S3 prefixes increases parallelism, allowing S3 to scale throughput more effectively. S3 is a highly distributed system, and by using distinct prefixes, you enable S3 to process requests concurrently across its internal partitions, overcoming potential per-prefix limits and reducing write contention. Enabling S3 Transfer Acceleration is for accelerating uploads over long distances via edge locations, not for improving throughput within the same region when network bandwidth isn't the bottleneck. AWS PrivateLink for S3 provides private connectivity to S3, which doesn't directly address throughput limitations for high-volume uploads. AWS Global Accelerator improves application availability and performance for global users, not S3 upload throughput within a single region. Disabling encryption is not a recommended security practice and would have negligible impact on throughput compared to parallelism.