This might be well-known, but today I learned something: If you're planning on growing a vdev by replacing the disks with larger ones, and you have enough interfaces to hook up all of them at the same time, you can replace them all at once. And it runs at the same speed as replacing a single disk. It should be perfectly safe, because the original disks will remain online throughout the operation.
I got the idea from Chris Siebenmann's blog post: https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSMultidiskResilversFree
(ignore the checksum errors on replacing-0, they're from an interrupted previous single-disk replacement)
My existing raidz2 vdev is da9-da15. The replacement disks are da1-da3 and da5-da8.
I got the idea from Chris Siebenmann's blog post: https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSMultidiskResilversFree
(ignore the checksum errors on replacing-0, they're from an interrupted previous single-disk replacement)
My existing raidz2 vdev is da9-da15. The replacement disks are da1-da3 and da5-da8.