title: How to create a mirrored zpool after adding a drive to zpool?
body: <p>I had a zpool with just one drive, with some content in it. I was willing to add a second drive as a mirror one but instead of "attach" command I used "add". </p>
  
  <p>I still didn't use the pool after adding the second drive, but trying to removing it return:</p>
  
  <pre><code>$ sudo zpool remove bck2016 sdc1
  cannot remove sdc1: only inactive hot spares, cache, top-level, or log devices can be removed.
  </code></pre>
  
  <p>Trying to force attach result in:</p>
  
  <pre><code>$ sudo zpool attach -f bck2016 sdb1 sdc1
  invalid vdev specification
  the following errors must be manually repaired:
  /dev/sdc1 is part of active pool 'bck2016'
  </code></pre>
  
  <p>The current status is:</p>
  
  <pre><code>$ sudo zpool status
    pool: bck2016
   state: ONLINE
    scan: none requested
  config:
  
      NAME        STATE     READ WRITE CKSUM
      bck2016     ONLINE       0     0     0
        sdb1      ONLINE       0     0     0
        sdc1      ONLINE       0     0     0
  
  errors: No known data errors
  </code></pre>
  
  <p>How can I transform this pool to a mirrored one?</p>