Unavailable drives? Check your cables first.

[Palladio]

Two drives in my RAIDZ2 pool went Unavailable today. I took them out of my case (Fractal Node 804), and found damage to two SATA power connectors - not sure how it happened, but the plastic was cracked and the metal contacts weren't contacting the drives' contacts.

I replaced the SATA power cable with another compatible one (Seasonic Prime Gold PSU), booted, and my pool was fine. Lesson learned!