> Having a thin provisioning would be great, expecially for the 4TB disks (because i'm sure that 4TB is just a "max recomended sizing" that the "app vendor" wrote in some document for his application sizing)
What's provisioned on storage are...
> Battery backup of a single cache still makes it a SPOF
No, it doesn't.
In your scenario, another, prior and unaddressed, failure is required to make NVRAM (and/or other component(s)) a potential single point of failure.
It doesn't make it a...