I have a 2-drive zfs pool created in mirror mode. Now I've managed to get my hands on a third drive, and I was wondering if I could add the drive, and change the pool type to raidz, which is pretty much better for three disks.


No, you can't do this using normal tools... at least not without lots of pain and risk.

If you have the option, you should go to 4 disks and RAID 1+0 or offload the data and recreate the pool the way you want it to look.


the short answer No.

the longer answer. With going from 2 to 3 drives you can do the following.

Step 1. Break the mirror by detaching one of the drives.
- this should give you 1 drive with the data in the 'mirror' pool
Step 2. Create a fake drive in the form of a sparse file
Step 3. Create a new Raid-Z volume with the new drive + the previously detached drive + the fake drive
Step 4. Degrade the array by removing the fake drive, leaving you with the 2 actual harddrives in the array.
Step 5. Copy all data from the old pool to the new pool.
Step 6. Remove the old mirror pool, and add that drive to the RaidZ pool.

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