I strongly disagree. If I have an 8 disk server at home with mirroring, the pool could only take a single disk failure. The usable space would be 50% of the total disk. Further, I'd have to buy any extra disks in pairs.

If instead I ran RAID6, I'd have 80% of the disk available and I could add disks in single disk increments.

I think ZFS makes great sense for businesses that can throw money at disks but for smaller businesses or home servers it's kinda bad.

I think it's not a very good idea to design storage solutions around how inexpensive it is to add capacity to them. Your 9+-drive RAID6 is going to take forever to rebuild; 4+ mirrored vdevs (or mirrored RAID of course) will not be a problem at all.

I run a FreeNAS device at home (ZFS underneath).

It was kind of a pain to configure (albeit quite flexible) but it's been pretty nice overall, already survived 1 disk failure and a capacity upgrade (during which I had to resilver after every individual disk upgrade, which was time-consuming, but after the last disk got upgraded, the extra space finally showed up)

You also wouldn't get the same I/O performance a stripped mirror will give you. You can get extra resiliency using a three disk mirror.

Disk is cheap. There's no reason to design like it's not.

Disk is at least ~$0.023/GB. Whether it's "cheap" or not depends on how much of it you need.

Plus, disk may be cheap but servers to house it are not (the kind of servers you'd run in your house, I know you can get cheap SC846 off eBay).

Servers can be inexpensive. It really depends on your use case. You don't have to drop 50K on a box to make a killer ZFS storage array.

My scale starts at 40PB with a "P". Disks aren't cheap.

I use stripped mirrors for most of my ZFS deployments. Disk is cheap. If you want more resilience do a three way mirror.