I have a pfSense box with a 2-drive RAID-1 using gmirror. Recently, a drive failed, and I replaced the drive, and the RAID-1 is now back to normal. But this incident also made me interested in setting up a 3-drive RAID-1, just for the extra redundancy.

Anyway, I figured it would be extremely easy to do this. Just attach a 3rd drive to the box and use gmirror insert to add the new drive to the RAID.

So, I attached a new disk (of the same size as the other 2) via serial ATA to the pfSense box. Upon reboot, the disk appeared there in /dev as ada2.

So, before I attempted to add the new disk, gmirror status showed the following:

                Name    Status  Components
mirror/pfSenseMirror  COMPLETE  ada0 (ACTIVE)
                                ada1 (ACTIVE)

Then I typed:

gmirror insert pfSenseMirror /dev/ada2

After that, I checked the status again with gmirror status, and it showed:

                Name    Status  Components
mirror/pfSenseMirror  DEGRADED  ada0 (ACTIVE)
                                ada1 (ACTIVE)
                                ada2 (SYNCHRONIZING, 0%)

So it looked like everything was going well ...

But then, a few minutes later, I check gmirror status again, and now it shows:

                Name    Status  Components
mirror/pfSenseMirror  DEGRADED  ada0 (ACTIVE)
                                ada2 (SYNCHRONIZING, 9%)

So... WTF? It looks like it kicked off drive ada1 from the RAID for some reason.

So, what exactly is going on here? Does gmirror inherently limit a RAID 1 to only 2 drives? Or did I do something wrong here?


Under the examples of gmirror syntax is provided for creating a 3 disk mirror. Apologies for missing it before.

  • Although all of the examples show only 2 disks, I don't see anywhere where it explicitly says gmirror is limited to 2 disks only. Can you elaborate a bit on where it says this in the man pages? – Siler Dec 4 '17 at 21:13
  • I was about to edit my post, I skipped right over the example of a 3 disk mirror in the gmirror manpage.. – Confusias Dec 4 '17 at 21:19

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