It's hard to give a good estimate on how much system resources (such as CPU, RAM, or disk space) Mastodon uses, because it depends so much on how you use your Mastodon instance. Having too little of any of these can cause issues, leading to things failing in unexpected ways. Here are some signs you're running out of resources and should upgrade your plan.

The Signs Are In Order

Every user on your instance puts additional strain on the server. Much like a post office, Mastodon needs to deliver posts to their addressees in a timely manner, and it keeps a queue to prioritize its tasks.

Mastodon handles local tasks first (interactions between users on your instance, new posts, etc.), then remote tasks (posts from other instances, interacting with users on other instances), then email delivery for new member signups, and then maintenance tasks like backups, cleanup, and trends.

Tasks will fail from the bottom up. So, if people report that they aren't getting signup emails, then local and remote tasks are taking up all the server's capacity. If your users can only see each others' posts and not posts from people they follow elsewhere on the fediverse, then your local tasks are bottlenecking the instance.

If any of these are failing, chances are that your current resources are insufficient, and you may want to upgrade to a higher plan.

Storage space

Mastodon stores anything its users upload on your server. With Fedihost, all storage on your account is shared, and Mastodon will store uploads in this space. If your users post a lot of pictures or especially videos, then you may run out of storage faster than expected.

Also, Mastodon makes a copy of any media from posts it knows about, so that when your instance's users see those posts, it doesn't need to download the media files over and over again. These get routinely cleaned up on old posts over time, but too many can overwhelm your storage capacity.

It can be hard to tell when you've run out of storage. If large uploads are getting rejected, or if you can't post or see others' posts at all, you may want to log onto your Fedihost dashboard and see if your storage is full. If your storage is full, don't wait to either clean up your storage or upgrade your plan! If things start failing, then it could break federation, causing other issues down the road.

Good habit: Monitor your Fedihost storage frequently by logging in to your dashboard and checking your storage usage. That way, you won't be caught by surprise running out of storage.

Caution: Relays

When setting up a new instance, joining a relay can be good to find new posts, but be careful about joining one that's too big. Joining a relay means that your instance can see all posts from that relay - and your instance will download all the media content. This can be fine if your relay is mostly instances of a similar size, but join a relay with huge instances and you'll run through your storage space in no time.