I have 2x 2TB drives setup in a stripe configuration. Currently have <1TB of data on this stripe. I want to convert these to a mirror. Can I accomplish this in the gui? I didn’t see many options in Storage>Disks.
You would first have to remove one of the disks from the pool. Better to choose the one with least data on it. Check with zpool list -v <poolname>
The data will be evicted and saved onto the remaining disk.
Now you can use the removed disk to “extend” (attach) the single drive into a 2-way mirror.
Do you have a backup of your data? Is it not feasible to create a new pool from scratch and replicate everything over from a backup source?
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Great, thanks for this. I can’t figure out how to remove a disk in Storage>Disks. Can I do it from there?
Yes, I do have a backup and starting from scratch does seem easier, but less fun! I may still go this route. To do this I would just remove both disks, then add them back? (Again, haven’t figured out how to remove a disk)
You have to do it from the Storage → VDEVS page. Be very careful.
No. There is no “adding them back”. You would essentially destroy the pool and do a quick wipe on the disks. Then you create a new pool from scratch and replicate everything over.
You can try the first approach, since you won’t need to copy or transfer any data.
The safer approach involves a third disk, which is used to make a mirror (Storage>Pool> Extend) with one of the stripe members, and the you remove the other stripe member.
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I guess you mean Storage>pools. For there I can select Pool Status and select one of the disks. I think I then want to Offline disk #1. Then Extend disk #2 to the offline disk #1? Sound about right?
This does sound alot safer, unfortunately I do not have a third disk.
You don’t need a third disk if one of your current disks uses Quantum Storage™. It can be full of data and empty at the same time.
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No. You want to “Remove” one of the disks. You technically have 2 vdevs and want to remove one of them. Whichever you remove, all its data will be evacuated to the remaining vdev (single disk). Now your pool with be comprised of a single vdev (single disk). You can “Extend”[1] this single-disk vdev to convert it to a 2-way mirror by using the previously removed disk.
It makes more sense to remove the vdev (single disk) that has less data on it. You can check with zpool list -v <poolname>
The TrueNAS GUI and tooltips use strange names. “Extend” is really the
attachsubcommand inzpool. There is noextendin thezpoolcommand. ↩︎
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Yeah, I can’t find a Remove option. I see Edit, Offline, Replace, and Extend.
Thank you, but I am just not seeing that. I’m on Core, maybe you are using Scale?
If I go to Storage>Pools>[pool gear] there is an Export\Disconnect option. It gives me a pretty severe warning when I click on it, but maybe this is the way to Remove it from the pool?
Which version?
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With an SSH session, what is the output for these two commands?
zpool status -v <poolname>
zpool list -v <poolname>
As @dan requested, the version of Core is important too, since older versions did not support this feature.
version 13.0-U4
root@freenas:~ # zpool status -v Spare
pool: Spare
state: ONLINE
status: Some supported and requested features are not enabled on the pool.
The pool can still be used, but some features are unavailable.
action: Enable all features using ‘zpool upgrade’. Once this is done,
the pool may no longer be accessible by software that does not support
the features. See zpool-features(7) for details.
scan: scrub repaired 0B in 00:41:43 with 0 errors on Sat Nov 15 04:41:43 2025
config:
NAME STATE READ WRITE CKSUM
Spare ONLINE 0 0 0
gptid/fa2eb3b1-98b2-11e8-90f1-0cc47a7558b5 ONLINE 0 0 0
gptid/90b7d36c-2f38-11ea-8442-0cc47a7558b5 ONLINE 0 0 0
gptid/90b7d36c-2f38-11ea-8442-0cc47a7558b5 ONLINE 0 0 0
errors: No known data errors
root@freenas:~ # zpool list -v Spare
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
Spare 3.62T 559G 3.08T - - 0% 15% 1.00x ONLINE /mnt
gptid/fa2eb3b1-98b2-11e8-90f1-0cc47a7558b5 1.82T 145G 1.67T - - 0% 7.80% - ONLINE
gptid/90b7d36c-2f38-11ea-8442-0cc47a7558b5 1.82T 414G 1.41T - - 0% 22.3% - ONLINE
Is the pool feature enabled?
zpool get feature@device_removal Spare
value=disabled 
Do you plan to import this pool into an older version of TrueNAS or ZFS? If not, you can safely upgrade your pool’s features:
zpool upgrade Spare
IIRC, this can also be done in the GUI from the pool’s page. Click on its cogwheel icon.