Mergerfs + Snapraid with existing external hdd

My 6TB external hdd (ext4) is reaching capacity and I am needing to expand storage. I weighed some solutions and want to go with mergerfs and maybe snapraid. My plan is to get a 4 bay hdd docking station and a single 18TB hdd formatted to use xfs. For now I want to use both 6TB and 18TB hdds together and be able to expand storage in the future. Eventually I hope to decommission the 6TB drive and just fill the other bays as needed. I am unsure if I should throw snapraid into the mix. If I make the 18TB hdd the parity drive, can it still be used to store data?

Quote from gderf

With respect to SnapRAID, you can store data on a Parity drive but it can't be protected by SnapRAID.

You don't say anything about the hardware you are running so it's difficult to provide meaningful advice about storage. Research any multi HDD docking stations you are considering. Make sure they present each disk individually to the OS. Many of these things don't do that.

I am targeting a Sabrent DS-U3B4.

Quote from Soma

Please, don't. That thing is not a proper NAS component.

4-Bay USB 3.0 SATA 2.5"/3.5" SSD/HDD Docking Station - Sabrent

I find it amusing the "Hot Swap" part but no Linux support.

Oh, and the "clone drives on a touch of a button" would be funny to see also on Linux (when there's no support for it)

If you do treasure your DATA and the reliability of the hardware, either buy a proper USB box or just go with a proper 4+ SATA connections MB.

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I know this one might not be in vogue but I just need to be able to expand storage without breaking the bank. If there is something better and cheaper, I am open to suggestions.

While losing the data would be annoying and inconvenient, it would not be the end of the world for me. My setup is pretty crude. I have omv hosted on a raspberrypi with a bunch of containers running. I am interested in mergerfs to make life easier. I don't think snapraid would be all that beneficial to me considering the nature of my data and initial setup but I think it would be interesting to learn. It doesn't even make sense to use snapraid for my use case unless I buy more hdd.