SMR on a z-mirror is quite a bit different than a raidz/2/3 setup due to how SMR works. A mirror will do much better at optimizing the writes for SMR rebuild. When using raidz, your milage may vary, as they say.
It absolutely will work. Before I knew the difference between SMR & CMR, and when WD obscured this on their reds, I bought SMR to use in a raid2 setup. I first noticed something was wrong when sequential write performance would begin to tank sharply on the drives and it wasn't due to the ZiL. Replacement of a failed drive was slow, very slow but I would work. After 5 years in service I replaced them with CMR drives one at a time. The replacement speed from the first to the last increase about 3x.
So don't agree with the doom sayers about SMR but for the few $ more over the course of 5 years, I'll go with the speed.
Yes, it will 'hurt' more to use SMR drives with raidz1/raidz2/raidz3.
... but I believe ZFS DRAID mode will not hurt that much on SMR drives.
In ZFS DRAID there is no dedicated SPARE drives - but 'spare blocks' are spread across the disks along with 'data blocks' and 'parity blocks' - this means that all drives 'read' for the resilver and all drives 'write' for the resilver.
Worth noting: During a zfs resilver (as with any sort of RAID rebuild) your drives are continuously busy. So the vastly-longer CoW/SMR rebuild can be rather problematic on production systems. Best to know your workload, and make sure that you have an ironclad paper trail - showing how PHB ignored your repeated objections and warnings when he decided to save money by buying SMR disks.
To be honest I would not expect using SMR drives in some important production systems.
I would even prefer to use CMR ones ... but the 2.5 drives with 4-5 TB capacity are only available in SMR - maybe in the future when 2.5 drives will ofeer 8-10 TB of space - there would be a 4-5 TB CMD 2.5 drive.
It absolutely will work. Before I knew the difference between SMR & CMR, and when WD obscured this on their reds, I bought SMR to use in a raid2 setup. I first noticed something was wrong when sequential write performance would begin to tank sharply on the drives and it wasn't due to the ZiL. Replacement of a failed drive was slow, very slow but I would work. After 5 years in service I replaced them with CMR drives one at a time. The replacement speed from the first to the last increase about 3x.
So don't agree with the doom sayers about SMR but for the few $ more over the course of 5 years, I'll go with the speed.