Howard Miller

There's some interesting hints embedded in this response...

You don't say what sort of environment this is... but I would caution you to consider whether it's a good idea to update plugins outside of a testing environment. They do have bugs and, occasionally, ones bad enough to bring your site offline.

As the saying goes, ask me how I know...

The first thing the upgrade procedure does is to purge all the caches. On a large site, it can take ages.

I don't know about opcache. I always use the cli for upgrading and have never had an issue.

No... the issue is that by default Moodle will cache to the shared file system. Moodle is now incredibly reliant on its cache - so if your moodledata is ridiculously slow then you will see exactly this sort of performance.

Moodledata itself doesn't make much difference to performance for simply uploading files and stuff.

My other concern is that he has configured the cache properly. The UI of that config page is pretty poor and you can be forgiven for missing the default assignments at the bottom of the page.

You and me both