MySQL on VM is gradually slowing down, what could be the reason?

Question

MySQL

The effect appears after a few months, approximately about six months. On a dedicated server, I do KVM virtualization and raise the virtual machine on a QCOW2 disk in the form of an image / file of a predetermined size. I start the database server on it and nothing else. Everything works well for a few months, and then it starts to slow down gradually - the number of slow Slow Log requests increases.
It would seem linear with increasing load, but no. If you do a reinstall of the virtual machine, everything is back to normal. I do not remember exactly, but it seems that the reinstallation of the OS on the physical server additionally affected it. It seems to me, or is this not a coincidence? After all, reinstalling the virtual machine / server once a quarter / six months is not an option. I would like to know the reason for this phenomenon. Can you suggest why this is happening?
Base about 20GB of requests it is a lot of. The tables are large, 25M rows each. Requests become slow regardless of their complexity and appear immediately in batches. Apparently, the problem is in the disk / image - but I don’t know what exactly. As I understand it, the disk response speed is growing, and with it, requests are slowing down.

Answer 1

I have been studying this issue for a long time, it's not a virtual machine at all. The trouble with any modern hypervisors that carry more than one virtual machine is disk sharing. What is your load average on the hypervisor? Surely, there is more than one virtual machine with MySQL?

Answer 2

don't use qcow first and optimize host and guest files