> 1. From my own experience, most people who use a ZIL for faster sync writes are wasting space. You only need five seconds of peak throughput (for a 10Gb connection that's ~5 GB). Create a pair of 25 GB partitions for the ZIL rather than dedicating entire devices.

You might benefit from the same technique for a "special" vdev... If you run an all spinners array, but the metadata is on a small partition, you might get better seek times during metadata scans, since everything will be closer together? And/or if you use raidz for your regular vdev, but mirror for the metadata, you'll have more capacity for metadata reads.

> Even my 24 TB NAS takes 24+ hours with no other activity

Your NAS sounds pretty slow, it shouldn't take an hour to scrub 1tb of data (on average)

Yeah, the only place I use SLOG is with Optane devices in front of SATA/SAS flash. Anything that needs the speed of SLOG shouldn't be on rust anyways.

I would be in a different world if my system was backing banking or other loss critical data. For all my workloads, losing 5 seconds of writes in a crash is NBD.