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Comment by yoasif_ | Hacker News Reader

The easiest way to do this is to use mirror vdevs, that way you can add disks two at a time. Of course, you miss out on RAIDZ functionality that way, but that's the simplest setup.

I've gone ahead and actually created a new array using btrfs raid10 instead (with an eye towards a RAIDZ2/3 like configuration whenever the btrfs guys get around to fixing it); btrfs allows for online reshaping of the mirroring configuration, so it doesn't have the limitations of ZFS in this instance.

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Agreed, mirror vdevs are the way to go. Here's a post that explains the tradeoffs between RAIDZ and mirror vdevs in great detail: http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-...

I'm still not sure what setup I have. I really should have written down every decision I've made while building my NAS (I think I've now found articles that disagree with every single choice I made)

    $ zpool status
  pool: BoxODisks
 state: ONLINE
      scan: scrub repaired 0 in 9h20m with 0 errors on Sun Jul 31 01:31:31 2016
    config:

        NAME                                            STATE     READ WRITE CKSUM
        BoxODisks                                       ONLINE       0     0     0
          mirror-0                                      ONLINE       0     0     0
            gptid/18059e22-b6a4-11e5-9cca-0cc47a6bbf34  ONLINE       0     0     0
            gptid/194649b1-b6a4-11e5-9cca-0cc47a6bbf34  ONLINE       0     0     0
          mirror-1                                      ONLINE       0     0     0
            gptid/1a86b3cc-b6a4-11e5-9cca-0cc47a6bbf34  ONLINE       0     0     0
            gptid/1bcd3ad6-b6a4-11e5-9cca-0cc47a6bbf34  ONLINE       0     0     0
        cache
          diskid/DISK-S24ZNWAG903847Lp1                 ONLINE       0     0     0

I think I have mirrored vdevs.

What does that mean for replacing failed disk/s? What does that mean when I want to upgrade to 8TB drives? The biggest "mistake" I made was buying a very expensive 4 bay enclosure - 4 drives is not enough.

When you want to upgrade, you can offline and replace each disk, then resilver, in turn. If the pool is set to autoexpand, you'll eventually get a total capacity of 16TB. You can do this for all the disks, or for each mirror separately in two groups of two.

I agree that mirror is the best (i.e. simple and easy) way to do it, and to avoid raid-greed (http://constantin.glez.de/blog/2010/01/home-server-raid-gree...). Mirror (vs Raid-Z) gives us better fault-tolerance and flexibility.

Can you do btrfs with FreeNAS? I didn't think that was available.

No, you have to go with Linux. I'm using the latest Ubuntu server LTS (since ZFS is also included, and because I'm familiar with Ubuntu).

I don't have experience with FreeNAS unfortunately.

If you could, that makes no sense. ZFS is superior.

Unless you want to reshape your array. Then md-raid is superior. Btrfs's raid implementation has had some pretty bad issues recently and has been declared "experimental" as a result.

This is inaccurate. Raid56 have always been labeled experimental, but recently, data corruption bugs were found which make it dangerous to use.

Other raid levels (raid0, raid1, raid10) work fine and are considered stable -- at least as stable as the filesystem itself.

Either way, if you care about the data, you must backup, no matter what fs you use.

Apologies, I only saw the recent mailing list post which basically said "we're removing the ability to even compile support for raid56". I didn't mean to say that btrfs was overly-zealous in their trust of new code (I personally am super excited for the future of btrfs).

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