> So it came as a surprise when sysadmins began noticing their new Western Digital Red NAS drives were dropping out of NAS RAIDs and ZFS pools owing to random write timeouts and failures.

I experienced exactly that a few days ago. I have some of those SMR WD drives in my NAS and one drive just disappeared from the ZFS pool while importing a large database. I rebooted and the drive was back. ZFS worked its magic and everything seems fine now, but it doesn't inspire confidence.