Wich is the biggest capacity HD I can stuff a 2014 Mini with?

[Kaikidan]

If everything goes right, at the end of the year i will be able to upgrade my main mac, and I plan to use my actual mini 2014 solely as a headless media server (something he already does while being used as a daily computer).

For this, I plan on opening him and putting the biggest drive I can manage to fit in the place of the native 1tb HD drive. Since it will be on 24/7 and will solely distribute media to the house I can use a cheapper HD instead of a SSD, I would like to put at least 4tb in it, conect it to power and thats it, no cables, dongles, external drives, nothig, just this nice 20x20cm box on a secluded place free to run 24/7. (and if the need arises, then i would plug a external drive)

Wich is the biggest HD size I can go without going with external drives?

 

[DeltaMac]

The biggest internal HD for a mini will be a 2.5-inch drive, at the most.
You can get those with more capacity than 4TB, however I am pretty sure that you would not be able to use the extreme largest capacities, as those drives may be too thick to fit inside the mini.
https://www.amazon.com/Seagate-BarraCuda-Mobile-2-5-Inch-ST4000LM024/dp/B01LZMUNGR/

So, I would say that you are basically limited to 2TB. There's several choices for that capacity.
Macsales.com has some of those: https://eshop.macsales.com/upgrades...r.dimension_drive_type_5=2.5" Notebook Drives

 

[Boyd01]

I would like to put at least 4tb in it, conect it to power and thats it, no cables, dongles, external drives, nothig, just this nice 20x20cm box on a secluded place free to run 24/7.

If it's hidden in a secluded place, why would you care if it has an external drive? I use a 2014 Mini for the same thing and it's hidden in a cabinet under my stereo system. Media is on an inexpensive 4tb external USB 3.0 drive with a second external drive that is automatically cloned every night for a backup.

I just don't see any advantage to an internal drive for this kind of use, in fact I think it's a disadvantage. My media disk failed after about 3 years. Just swapped it with the backup disk and was up and running in a couple minutes with no trouble. That would have been a big pain with an internal drive!

 

[Kaida]

If everything goes right, at the end of the year i will be able to upgrade my main mac, and I plan to use my actual mini 2014 solely as a headless media server (something he already does while being used as a daily computer).

For this, I plan on opening him and putting the biggest drive I can manage to fit in the place of the native 1tb HD drive. Since it will be on 24/7 and will solely distribute media to the house I can use a cheapper HD instead of a SSD, I would like to put at least 4tb in it, conect it to power and thats it, no cables, dongles, external drives, nothig, just this nice 20x20cm box on a secluded place free to run 24/7. (and if the need arises, then i would plug a external drive)

Wich is the biggest HD size I can go without going with external drives?

2TB if you are using the 2014 tray. 5TB if you change it to the 2011/2012 hdd tray.
https://forums.macrumors.com/threads/mac-mini-2011-2012-5tb-storage-ssd-idea.2016331/