Since you are talking about a virtual machine and not a physical one, I doubt any software tool will be able to tell you what type of disk it is, as that is abstracted away from the end user.
Also remember that VPSs have I/O constraints that stop customers using all of the disk I/O, so even benmarking software will only show you the throughput your host has allowed you to acheive.
When purchasing a VPS you need only concern yourself with this
- Does it perform well enough to do the job I am going to give it?
- Is it reliable enough to do the job I a going to give it?
If you are using a VPS to see how hard you can hit the disks, your fellow tennants won't want to share with you.
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