For 12 10TB disks, I'm looking at 2 possible ZFS raid configurations: 2 vdevs, each having 6 drives in raidz2. 80TB total storage with 40TB lost on parity. 6 mirrored vdevs. 60TB Total storage with 60TB lost on parity. I was almost sold on mirrors after reading this: ZFS: You should use mirror vdevs, not RAIDZ. | JRS Systems: the blog But now, I'm not so sure. The extra 20TB lost to mirrors kind of sucks, but I could live with that. The use case here is just NAS media storage, so mostly reads and few writes. What really bothers me is the possibility that if one disk dies, I lose the whole array if the other disk in that mirror also dies. With a raidz2, I can lose 1 of any other disk and still recover. I'm only really concerned with redundancy and the possibility of permanent data loss here. Extra IO performance during normal operation is nice to have but not so important. The tradeoffs appear to be: Mirror: (-) Only 60TB total storage (+) Resilvering is fast and only does reads on one disk, making it less likely to trigger a second failure. (-) Possibility of data loss if the other disk in the faulted mirror fails during resilvering (+) Upgrading the capacity of a vdev requires only 2 disks at a time and would run rather quickly. Only need to buy 2 disks to start. (+) Faster read / write performance (Not that important for my use case) (+) With only 5 mirrors, 2 drive bays are free, allowing for a hot spare. Raidz2: (+) 80TB total storage (-) Resilvering is extremely slow and does both reads and writes on all disks, making it more likely to trigger a second failure. (+) Possibility of data loss only if any 2 other disks within the same vdev both fail during resilvering (-) Upgrading the capacity of a vdev requires replacing 6 disks at a time and would take an extremely long time. Need to buy 6 disks to start. (-) Slower read / write performance (Not important for my use case) (-) No possibility of having a hotspare as the 2 vdevs consume all drive bays. Raidz is off the table as the industry pretty much fully agrees that its not suitable for large disks. Raidz3 would mandate making an entire 11 + hot spare or 12 disk pool. Meaning I'd have to spend a fortune buying 12 disks up front and in the future if I want to upgrade capacity I have to buy another 12 disks. For those of you with a raid setup, what raid configuration did you end up using and why? If you could go back, would you change it something else? Does anyone have a good estimate for how long it would take to replace a single faulted disk in a raidz2 array of 6 10TB disks? How about for a mirror of 2 10TB disks? Thanks!