How viable are Rasp Pi's for cheap NAS solutions ?

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As the title, I was just looking at NAS options saw that Raspberry Pi can be used, I'm just curious how viable they are as a budget option to NAS, would I still be able to have RAID options and the redundancy that comes with it ?

Also how would I go about connecting the drives as obviously a Pi runs off an SD card and doesn't have any Sata connections ? Would it be Sata->USB->Hub->Pi ?

I figure doing it this way would be more beneficial to learn the workings of NAS as opposed to buying a plug and play option from the likes of Synology, plus if it does the same job and is cheaper that's a bonus also

 

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Is a better option just going with a cheap mobo/cpu/ram + case then to avoid the USB slowness ?

It wasn't a lot I needed to backup just 3TB at the moment but I'll be needing more at a later date so may as well jump ahead of it and future proof myself by knowing how to do it all, so I'm not stuck when I do really need it

 

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Cheers guys, the XU4 option looks pretty good, do you just run your drives through a hub so you can get past the 3 USB port limitation ?

Will have a look at cost options for Dell stuff too or try my luck with getting something suitable off the MM