How to replace pool with different topology pool in scale?

TrueNAS General
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I have a TrueNAS SCALE server as my offsite backup. In order to connect back to my main site, I use Tailscale on that machine.

Currently, my App pool is a single USB drive. I would like to change that to be 2 drives in a ZFS mirror. When the App pool was created, TrueNAS scale wouldn’t let me create any VDEV type other than stripe, so that is what the current pool is using.

How do I migrate the apps pool to be a mirror on the 2 new USBs?

If I can move the apps to the boot pool then that would be even better, the boot pool is 2 mirrored proper SSDs.

Disclaimer:
The 2 USBs are different models purchased at different times from different manufacturers, and have been through different levels of use before. Because of the above, they are unlikely to fail at the same time. I’m using USBs because 16GB is already massive overkill for tailscale and I don’t really feel like having 100+ GB for the sole purpose of installing Tailscale.

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  1. You should be allowed by TrueNAS / ZFS to create a mirror of the single vDev single drive. No data migration needed. (Strictly speaking vDevs need to be mirrors or RAIDZ and yours is a single drive mirror.)

  2. However THIS IS NOT A GOOD IDEA. There is nothing stopping you from doing this but USB connections are not reliable and as soon as one of these drops it is likely that you will need to use the UI to initiate a resilver.

If you want to get the benefits of ZFS and TrueNAS you really do need hardware that is suited to it.

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How?

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In the UI - check the documentation web pages and if you are still uncertain come back and ask again.

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You can’t make a mirror with only a single disk, the UI won’t let you.
You can however make a single disk stripe and then Extend that into a mirror.

Source:

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They really need to use a different word. “Extend” makes it sound like you want to extend the capacity of the pool/vdev.

The tool should be labeled “Attach”.

Time to make a bug report that will get closed because I didn’t upload a debug file. :grin:

EDIT: I am in good company. Indeed I am.

@Stux @sretalla

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