Large database mysql 5.6 + linux, we want to update, can you help with advice?

Question

MySQL

We have 2 servers. One is under CentOS 6, the second is RHEL 6. Both servers have 4-6 TB databases.
In both cases we have mysql 5.6.
We want to upgrade, because the software is not new.
Stable work is a priority.
If the OS is more or less clear - upgrade CentOS and RHEL to 7, for example, then what to do with the DBMS?
Option 1 - Update mysql. Which release should you choose? 5.7 or 8? How will the OS and DBMS behave when both the OS and DBMS are upgraded?
Option 2 - Migrate from mysql to MariaDB. Again a question - what release of this DBMS to choose. And how will this simultaneous upgrade with the OS behave? What are the difficulties in migrating this rather big database?
Maybe there are some other pitfalls of this action, tell me colleagues pliz ...

Answer 1

1. Buy a server for software upgrade work.
2. Deploy the new OS there.
3. Install the latest mysql release.
4. Make a migration from an existing database.
5. Switch the link from the current OS to the new database.
6. After checking - set up the rest on the new one.
7. Make backups.
8. Turn off the old one, turn on the new one.
Old - use in the future as well.

Answer 2

Without staging, you, sorry, won't do shit.
At a minimum, you need to backup your junk before upgrading, whatever one may say.
To check that your structures and attachments will be transferred to the new version, you can make a backup without data, roll it out and check it out.
Well, the main question is what takes 5 ter in your database? Do you keep pictures there?