Switching between OpenZFS on Ubuntu and TrueNAS CORE with the same drives and zpool

[John Childermass]

I’d like to test drive TrueNAS CORE temporarily using a machine that normally runs Ubuntu and already has a zpool using OpenZFS. The zpool just contains documents and media files, i.e. I’m not using it to boot from or even to store a home directory. So, I’d be happy if I can just access those same files via TrueNAS.

I know that running TrueNAS CORE like this is definitely not optimal or recommended, but I just want to see whether TrueNAS CORE makes sense for me before potentially buying extra hardware.

I would plan to install TrueNAS on a USB-attached SSD and boot from that. Reading some older FreeNAS threads suggests that it should be possible to go from Ubuntu to FreeNAS and back, accessing the same zpool, as long as I export and import it each time. Is this still the case with TrueNAS?

Also, if I do not physically disconnect the (internal) Ubuntu boot drive when I boot into TrueNAS on the USB drive, can I tell TrueNAS just to ignore that drive, or will bad things happen? I am very aware I’m taking a risk by doing this, but would it work in theory, and is there anything specific I’d need to do?

In case it is relevant, the Ubuntu system has zfsutils-linux version 2.0.2-1ubuntu5.2 installed and modinfo zfs | grep ^version: shows “version: 2.0.2-1ubuntu5.4” (I’m not sure why one is …ubuntu5.2 and the other ubuntu5.4). "sudo zpool get version poolname" returns a VALUE of “-“ which I understand means it’s using feature flags.

 

[Ericloewe]

This should clear things up:

ZFS Feature Flags in TrueNAS

OpenZFS' distributed development led to the introduction of Feature Flags. Instead of incrementing version numbers, support for OpenZFS features is indicated by Feature Flags. Feature Flag states Feature flags exist in one of three states...

www.truenas.com

 

[John Childermass]

Thank you @Ericloewe! That's very informative. Do I understand correctly that if a feature flag is listed as supported, even if it's in bold, this means that TrueNAS supports it for read-write use from that specified version onwards, and the reference to "read-only backwards compatible" means that it's read-only in older versions? Or does it mean that if the document says "TrueNAS supports..." but it's in bold, then this means that TrueNAS only supports it as read-only?

 

[Ericloewe]

Bold means that you can import the pool read-only in versions of ZFS that do not support said feature.