H5serv doesn’t work directly with S3 storage since the HDF5 library is expecting a Posix file system. Using something like s3fuse (https://github.com/s3fs-fuse/s3fs-fuse) may work for read-only access to HDF5 files stored as S3 objects, but I haven’t tried this.
Anyway, as it happens, we’re currently working on a project for NASA to enable HDF Server to use object storage directly. The goal is to enable the HDF api across mutii-PB datasets hosted on S3. We’re about 6 months into the 2 year project, but it’s looking quite promising.