Today I found: Checking ashift on existing pools. In summary:
# zpool get all | grep ashift # zpool get all | less # zdb -C | grep ashift # zdb -C | less # zdb -U /etc/zfs/zpool.cache | less
Per ZFS 101—Understanding ZFS storage and performance you *really* want to make sure your ashift value is aligned with your disk’s sector size. ashift=9 for 512; ashift=12 for 4096; I’ve heard some SSDs can be 8K, but I haven’t been able to confirm for my own disks.