Simple mirroring (RAID 1) is my RAID choice for home FreeNAS setups.  My choice is a 3 drive mirrored RAID.  Quick summary below.

Why Mirroring?

• Simple
• Capacity is the same as a single drive. 
• The more disks the more reliability.
• Read speed is faster due to round robin reading from the mirrored drives.
• A 3 way mirror gives you 3x read performance.
• Write speed is the same as a single drive.
• Fault Tolerance via mirroring.
• A 3rd drive in a mirror gives you a hot-spare that is already synced.
• More Flexibility — Upgrading the pool with mirroring is easy, just zpool add.

Why Not RAID-Z?

• Most home RAIDs won’t have 4, 5, …, 8 or more disks.
• Generally Slower Read Performance than mirrored
•  Must access all disks for every single block of data, no gain, speed limited to the speed of a single disk.
• Corner Case: Streaming large amounts of data in parallel can be faster than mirrored, but this is not normal for home users.
• Write speed is the same as a single drive.
• Fault Tolerance — a higher probability that we lose data
• More disks means higher probability for a failure.
• Disk Failures means you need to get a replacement quickly, more quickly than a mirror.
• Less Flexibility — generally once your set your RAID it’s set.
• It can be changed but it’s complicated.

Reference:

• resilvering – the act of recreating data on a drive added to the pool.
• RAID-0 – basic striping. All disks work as 1 giant disk, no fault tolerance.
• MIRRORING / RAID-1 – basic mirroring.  Every disk has the same data.  The more disks, the more reliability.  Minimum of 2 disks required.
• RAID-Z / RAID-5 – n-1 space, 1 parity disk for fault tolerance. 1 disk failure, before you lose data.  Reads and Writes about the same speed as a single disk.  Minimum of 3 disks but 4 recommended.
• RAID-Z2 and RAID-Z3 – same as RAID-Z but with 2 or 3 disks for pairty.  This equates to 2 or 3 disk failures before you lose data.  Minimum of 5 and 8 disks respectively.
• RAID-10 – RAID 1 + 0.  Mirrors then stripes data.  Minimum of 4 disks required.

Links:
https://constantin.glez.de/2010/01/23/home-server-raid-greed-and-why-mirroring-still-best/
https://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
https://www.ixsystems.com/community/threads/mirroring-vs-raidz2-resilvering.43230/

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