Sharing a database among multiple devices

I’ve got an Odroid C4 running CE, with a 4TB hard drive attached. This works great, but I want to put the database on the Hard Drive too, so that one or more Kodi devices can access my C4 through the LAN, and have the database of movies and tv shows, thumbnails, and watched information accessible. Can this be as simple as configuring CE to put it’s database on the local HD, and have other devices configured to access it? Is there an easier or better way to do it? Currently I have a Fire TV Stick 4K accessing the shared movies and tv shows on the C4, but watched info is not shared, and the database has to be created and updated separately.

Have you looked here?

Install MariaDB server on your device. It can be one of your CE devices or NAS.
Add to advancedsettings.xml on all your CE devices the following section:

<videodatabase>
	<name>MyVideos</name>
	<host>192.X.Y.Z</host>
	<user>yourMariaDBUser</user>
	<pass>yourMariaDBUser'sPassword</pass>
	<type>mysql</type>
	<port>3307</port>
</videodatabase>
<musicdatabase>
	<name>MyMusic</name>
	<host>192.X.Y.Z</host>
	<user>yourMariaDBUser</user>
	<pass>yourMariaDBUser'sPassword</pass>
	<type>mysql</type>
	<port>3307</port>
</musicdatabase>

Thats it.

Thanks for the responses. A few quick questions:

Does MariaDB run well on the Odroid C4?
Is it generally reliable?
Are the thumbnails also stored in the database?
If I make this change on my main device, do I lose my existing database? Can I migrate it to MariaDB?

Don’t know about C4 but I don’t see a reason why it shouldn’t run.
Usually both tables (MyMusic82, MyVideos119 - Kodi 19.4) are small.
In my case around 35 MB in total and I have quite big library I would say.
I have database on my Synology NAS and do not see a reason why it should not be reliable when it is located on one of your Kodi devices.
No. Thumbnails are locally stored on each device. In database there are only links stored with information from what http they are downloaded. As the result: if you scrap your movie it will download thumbnails for it and the same thumbnail will be downloaded on your other devices.
For how to migrate your library database content to new MariaDB database - search for internet. There is plenty articles for a lot of scenarios. Google: “move kodi database to mysql” or “move kodi database to mariadb database”, etc.

Personally I use mariadb docker. It’s easy to move it around

I remember it being hell using a db, as they would change db versions between Kodi versions, so if you had different clients running different Kodi versions it wouldn’t work. That’s why I started using Emby as the db and all the management and just using the Emby addons on the clients.

Can the Emby server be installed on the C4 along with Kodi?

You can install it under Services. If it performs well on a C4 I don’t know. I have it installed on a Windows server.