This assumes that you have both pools setup and connected to the same system, but the replication steps can be done between two systems and the disks moved after replication (this would apply in the instance where the primary machine doesn't have enough ports to handle the additional drives for the second pool).

Assumption is that:

• tank: is the primary dataset name.
• temp-tank: is the name for the new pool prior to data migration.

The steps in a nutshell are replicate from tank to temp-tank, remove (or rename) tank, and then rename temp-tank to tank.

The process is quite straight forward, copy the data off the pool using ZFS so we preserve all the file permissions and everything, destroy and recreate the vDev and pool, and move everything back as it were.

Take a backup of the system configuration.

Navigate to System.

• Select the General tab.
• Click Save Config.

1. the system dataset needs to be moved off of TANK. Use the GUI to select a new location other than tank or temp-tank.

2. Create a system config backup using the GUI. This will be needed later, because when you detach tank, you will lose your share, snapshot and replication settings.

3. Use the GUI to create a snapshot of the dataset you want to move. If you want to move everything, select the root dataset. For flexibility in the future, I'd suggest checking the “recursive” option. Also, minimize use of tank. You will want to pick a time where nothing is changing, then ensure you have a snapshot, and then wait for replication to finish. The amount of time this will take depends on how much storage and the speed of your machine. It took ~36 hours to move 20TB locally for me. [ alternatively, you can use the CLI to create the snapshot and then replicate manually. “zfs snapshot -r tank@migrate” and then “zfs send -R tank@migrate | zfs receive temp-tank”]

4. Once replication is complete and you are satisfied that all data is on temp-tank it's time to detach both tank and temp-tank. Use the GUI to “detach volume” for tank and then repeat for temp-tank. When the confirmation window pops up DO NOT CHOOSE THE OPTION TO DESTROY.

5. using the CLI (or SSH) run the following to import and rename “zpool import tank old-tank” and then “zpool import temp-tank tank”. (for reference: zpool import [old-pool-name] [new-pool-name-name])

6. Once the pools are renamed, export them at the CLI “zpool export old-tank” and “zpool export tank”

7. Using the GUI, go to the storage tab and select the import volume tab and import tank. This step is what enables freenas to understand and control the pool.

8. Once the pool is imported, you can either manually recreate your shares, or you can restore from the configuration backup we made in step 2.

9. I would verify that everything is working to your liking before doing anything with old-tank. For safety, I'd leave it un-imported until you decide you need it or want to get rid of it. If you want to get rid of the data on the disks, I would import old-tank and then once it is in freenas, select the detach volume option for old-tank and this time select the destroy data option to blank out the drives. This is the point of no return, so know what you are doing before confirming.

[edit: note to self - here's the link to a great post on how to move Jails: https://forums.freenas.org/index.ph...-volume-to-new-ssd-volume.42105/#post-271740]