Actually it's better to just do mirrors. Avoid RAIDZ at all costs if you care about performance and the ability to resilver in a reasonable amount of time.
two sets of say 5 disks in a mirror raidz1 would still fail if a disk in one set failed and a disk in the other set failed. I guess you could do a stripe setup of 5 sets of 2 disks in mirrors. Still it seems wicked risky to me. I do agree though mirroring has been the best for speed but a lot of that changes with nicer SSDs especially NVMe ones.
I was curious about what a "nested" mirror is really. What exactly is nested?
I'd setup a large pool with mirror vdevs, i.e. n sets of 2 disks per mirror.
My half-remembered reasoning was that backups manage the risk you'll lose data. But replacing a disk in a mirror vdev is much easier, and faster, than doing so with RAIDZ.
The risk of RAIDZ is that resilvering impacts multiple vdevs, is much more intensive than a simple mirror resilvering, and thus the probability that additional drives will fail is much higher.
Here's a blog post that I definitely read the last time I was reading up on this:
I wonder if resilvering is still an issue with SSDs. But I cede your point, nested vdevs of two disks making mirrors makes sense. It doesn't sit well still, but makes sense
