Hello everyone. First of all I would like to say I am far from being an expert on drives or ZFS, so please forgive me if I make stupid questions.
I had setup a home NAS running on al old computer I had on my parents’ house. It was an easy setup, nothing to complex or professional, as the only purpose I needed it to fulfill was to use it as a personal cloud to store my files and be able to access it remotely using a VPN (I study abroad so it was just convenient). It ran TrueNAS SCALE and had 2 2TB drives configured in MIRROR so that I wouldn’t lose the data if one of the disks failed (or so I thought). It worked perfectly for almost a year, but a couple of days back I got a warning message saying that the pool status changed to degraded. Taking advantage of a short visit I made to my home, I checked on the NAS and figured out that one of the disks had completely failed (now reading I believe it was not suitable for the use I was giving it), so I detached it, and the pool was working fine again, just with a warning that said there was no redundancy. At this point, I thought of buying a new hard drive and restoring the pool as I had it before, with 2 drives on mirror. The problem is that, while I was waiting for the new drive to arrive, I decided it was a good idea to upgrade the TrueNAS software version, as it was recommended to have the latest version. After the reboot of the system, the pool now appears offline and the only disk I had is unassigned.
At this point I started researching and I’ve seen that I am not the first one to have this issue, I just can’t get any conclusions on how to retrieve the data. I know for a fact the data is still on the disk, because the pool appears as exported, and if I tried to create a new pool with that disk a warning message appears saying there is information on that disk that will be deleted. If I try to import the pool, an error occurs (I believe is an I/O error, but I’m not 100% sure right now)
My only question is: is there any way of retrieving the data on that disk/pool, or is it gone forever?
Thanks in advance to everyone and apologies for my ignorance 
PS: Obviously I’ll be more than happy to rethink the whole thing and correct my mistakes if you tell me so after recovering the data.
