I seriously doubt this is correct. It is common for database engines to install directly on raw block devices, bypassing the Linux kernel and effectively becoming the filesystem for those storage devices. Why would S3 work any differently? There are no advantages to building on top of a filesystem and many disadvantages for this kind of thing.
It would be a poor engineering choice to build something like S3 on top of some other filesystem. There are often ways to do it by using an overlay that converts a filesystem into a pseudo block device, but that is usually considered a compatibility shim used for environments that lacking dedicated storage, at the cost of robustness and performance.
It would be a poor engineering choice to build something like S3 on top of some other filesystem. There are often ways to do it by using an overlay that converts a filesystem into a pseudo block device, but that is usually considered a compatibility shim used for environments that lacking dedicated storage, at the cost of robustness and performance.