and how many cloud or VPS providers allow you to bring your own OS? And also split vda into multiple disks?
I'll tell you how many, zero, unless you're willing to pay premium and I mean vastly overpriced
Every cloud provider allows you to bring your own OS and configure disks in any way you want.
May be you're thinking about cheapest VPS possible, driven by something like cpanel. Those are not cloud providers. But usually you wouldn't choose them for reliable service, because their whole model is overselling.
