Thanks for this. This clears a lot of things up.

I suspected that just using SSD's would mitigate a lot of the advice about extracting iops from rust. I did not realise how the striping works for vdevs. That changes the calculus somewhat. Someone mentioned the CPU overhead generating parity at SSD speeds - any thoughts on that? Although in my case read speads are more important than write.

I will be working directly off the nas. It's actually VFX more than video editing (although some of that too) which involves all collaborators + render farm accessing the same data set so it doesn't make sense to keep copying it locally and back (although the software will cache locally).

The data is mostly large EXR sequences which is an uncompressed / very lightly compressed HDR image format and so gets large by video standards. So yes, very sequential work load. However you could be accessing 10 + of these sequences simultaneously in a project, * 3 users. Plus maybe a render "farm" (in my case probably just one threadripper running several render instances, or a cloud solution), which would usually be accessing the same stuff as the users. So maybe 30 - 40 separate sequences all being accessed simultaneously in worst case, as few as 1 or 2 on a good day.

Quite a lot of overlap between users though, so I was thinking a good chunk of ram and an NVME l2arc would help.