I'm a tier zero cloud engineer.
There isn't one file system used everywhere. I spot checked two providers and Google cloud VMs use EXT4 by default, Oracle Cloud Infrastructure VMs use XFS. And the underlying filesystem of the hosts could be different. Then there is the storage backend. And that uses a completely different filesystem entirely. Most decisions in the cloud are based on two things.
- Reliability
- Compatibility
Our number one priority is uptime, followed by adoption. So first we want whatever is going to be as stable as possible. Performance is typically not really as strong a consideration unless there is a problem. Typically we know what performance we should be getting, and we only address performance concerns if we're not meeting expectations. Additionally, most performance trade offs are small. Typically insignificant. And when you're talking about the cloud, most performance problems can be solved by more hardware. Imagine for example if one filesystem performs slightly worse than another, but is more reliable. We would rather take the reliable file system and throw a few more servers at the problem, than use the performant file system. Better uptime is typically worth more than the performance gains of something like a different file system.
