Downgrading SCALE version with newer version of pool

[Patrick_3000]

I recently updated from SCALE Bluefin to Cobia, and when I did, I was notified that the pools could be upgraded to a newer version, which I believe probably meant Open ZFS 2.2, in a one way operation. I went ahead and upgraded the pools.

Now I realize that I was too quick to upgrade to Cobia because there is a bug with MAC addresses for virtual adapters that I have opened a ticket on. I can work around the bug if I need to do so, but I'd rather not. It would now be my preference to downgrade SCALE back to Bluefin, which is easy to do through the boot menu.

However, I'm worried that if I downgrade to Bluefin, there will be a problem because my pools have all been upgraded. Does anyone know if this is a real concern? That is, will I run into problems if I downgrade to Bluefin even though my pools have been upgraded to what I believe is Open ZFS 2.2? (Or alternatively, can I roll back to the pools to an earlier version of ZFS?)

 

[winnielinnie]

If the upgrade enabled features that the older version of ZFS cannot support (nor is there a backwards compatibility on the feature) then you simply cannot import the pool.

One useful trick of ZFS (though sadly unappreciated or unknown) is the "pool checkpoint" tool.

Before doing an update or upgrade, you can make a checkpoint of the pool itself, which can be rewinded during import if something goes wrong. This will even undo any pool feature upgrades.

(Just keep in mind that anything done after the checkpoint will be lost. It's also wise to delete the checkpoint if everything seems fine. You don't want to sit on a checkpoint beyond the time you make a decision on whether or not to rewind.)

 

[joeschmuck]

I do my best to never upgrade the feature set unless I know there is something that would benefit me. I dislike the fact that you cannot roll back, well unless that pool checkpoint is created. I seen it posted before but I have not read about it. Time to read.

 

[Patrick_3000]

Thanks. It sounds like I'm stuck and cannot downgrade the pools so cannot return to Bluefin. That's OK, though not ideal. Hopefully the bug that I opened a ticket on will be fixed in a future version.