Since you are already on GCP, why not use their storage service for that? Another option would be to build your cluster with GCP computing instances and MinIO (https://min.io/) or to go with Backblaze (https://www.backblaze.com/). In both cases, you have an S3-compatible API; just with MinIO, you have more things available, like custom policies, hooks, and various integrations. And it is fast. Like very fast.