Thank you very much for your continuing to help me with my problem R6Mile!To be honest, what I would actually recommend for you - given that you seem to need a lot of storage, and that Thunderbolt 1/2 is very expensive - is pay someone to install two new drives in your Mini: one small SSD to be your boot drive (128/256GB should suffice) and one larger HDD (1TB/2TB? up to you) for your data. Probably the easier and most sustainable solution.
I would not consider Firewire for a boot drive - I use it just for data storage and its ok for that, but probably not suitable for boot.
I want to fix this problem myself as it's too expensive for me to get it repaired by a professional. It seems the 'dual internal 2.5" HDD' seems delicate and I'm worried about damaging my Mac Mini mid2011!
Just so it's clear in my mind: If I were to buy a Thunderbolt 1 external enclosure would I just need to connect a 2.5" or 3.5" internal HDD to it and it'd be ready for use or is there more work to it? I'd like to get my Mac Mini mid2011 running ASAP so I can use it as much as I can because the High Sierra security support ends soon... 😢
I'm leaning toward installing a single 2.5" internal HDD as I'm finding Thunderbolt 1 enclosures hard to find...