Use a SD Card or only SSD for NAS?

Hey everyone, my PI 5 will soon arrive. I have also bought a Crucial x9 pro 4TB portable SSD. I will just use this PI as a NAS with plex or jellyfin. Is it best to install both the OS and store the media on it or should I install the OS on a SD CARD and keep the SSD as a pure media storage space? What's the best solution to keep it as simple and fast as possible? And of course the longest lifespan as possible.

well it would work either way

if you put the os on a SD card it would leave even so slightly more space on the SSD, and you could have it sorted better

I don't know about that, both would work fine and if one is better it wouldn't be by much

Skip the SD card, they are more prone to fail.

I would have said this but I thought because nothing much is being changed on the SD card too much it's unlikely to fail

it's only being read that's it so it's unlikely to fail right?

The SD cards is fragile and it's not just read/write it is also power failures and time.