block: Change default IO scheduler to deadline except SATA

I am wondering if CFQ as default scheduler is still the right choice. CFQ generally works well on slow rotational media (SATA?). But often underperforms on faster storage (storage arrays, PCIE SSDs, virtualized disk in linux guests etc). People often put logic in user space to tune their systems and change IO scheduler to deadline to get better performance on faster storage.

Though there is not one good answer for all kind of storage and for all kind of workloads, I am wondering if we can provide a better default and that is change default IO scheduler to "deadline" except SATA.

One can argue that some SAS disks can be slow too and benefit from CFQ. Yes, but default IO scheduler choice is not perfect anyway. It just tries to cater to a wide variety of use cases out of the box.

So I am throwing this patch out see if it flies. Personally, I think it might turn out to be a more reasonable default.