How to pool HDDs without having them all spin up?

I would like add a bunch of SATA HDDs into my HTPC and turn it into a NAS. The HTPC is running Ubuntu 16.04 LTS

To have a safety net for HDD failures, I will be using the SNAPraid with one parity HDD.

I want to create one big pool out of the HDDs, for ease of access and I also want to be able to easily add more HDDs later.

Since I will be using snapraid, then even though the HDDs will be pooled, I still need to be able to access them individually too (so the snapraid can function properly)

In addition to this, when I access the pool I don't really want all of the HDDs to spin up, since that would be a waste, only those whose files I will read or modify should spin up.

Is there any not too complicated piece of software for Ubuntu which can do these things?

Thanks