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Excellent question!

Reality, is I can do both at any time. But leveraging ZFS I can have a lot of dynamics on how I use devices. My target is 5 x NVMes of 4TB each... and 12 x HDD disks for backups and lower performance things. Everything can be "mixed" within ZFS, so I can either create a RAID 0 of the 5 NVMes... or a RAID5... or 6...

On the 12 disks, I will be creating a RAID6 most likely (10 disk + 2 parity), and because how ZFS is built, if I need some cache for the raid, I can just slit a fast USB3.1 PEN into the system and get some fast IO's out of it.

It's quite dynamic and that's what I usually look on a system when I don't know exactly where I will be landing in terms of requirements. But obviously, I need to have some good level of hardware... bugs or incompatibilities (usually a role on the exploration of the edge tech) can bring you more set backs than progresses. So, a balance is key in hardware. Not always the cheapest per core/performance is the key.