Thanks everyone for the response and support, i really appreciate the efforts from everyone here, in additions to all my feedback regarding the issues with the truenas server, it was not originally setup by me, so i don’t really understand the structures of the hard drive in the raid, all i can say is that the server has 3TB x 10 Hard drives, and about 24TB is configured to act show as single disk to the truenas, and the person that setup the truenas originally is not reachable at the moments, so thanks everyone
I am not sure that asking the person who set it up in the first place is going to allow you to recover the data, but it can’t help to ask him anyway.
One more point before we close this:
Since you now effectively only have the operating system, you may want to think about rebuilding the O/S from scratch and / or upgrading it from CORE to SCALE because (assuming that you will want to do this at some point anyway) doing it when there is no data on the system is marginally lower risk.
Please do come back (and open another thread) if you have any more questions. You might find that it will lower the future risks to come back anyway and get our advice on e.g. pool configuration before you rebuild it.
Good luck.
P
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Knowing that upfront would have helped us help you.
That’s still a bad setting, but if there’s some redundancy in the harware RAID there might be hope.
If you have a backup, restore from there.
If not, then reboot to access the RAID controller interface from the BIOS and see what it reports about the ten drives.
For reference, the 10 drives should’ve been provided directly to TrueNAS, and TrueNAS should’ve been used to create the pool on 10 drives.
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What @stux said PLUS they need to be provided to TrueNAS in AHCI mode and not RAID mode - hence my previous advice to flash the LSI firmware to IT mode.
I know I have been pessimistic about recovery in previous comments, but this comment prompted me to consider a new possible cause - that the RAID card lost the stored RAID configuration
If this is the cause, then IF you can determine the correct configuration (because the person who originally set it up has kept some documentation - or by trial and error selecting the correct sequence from the 3,628,800 possible sequences of the 10 drives) then you might be able to get the data back again…
On a free weekend or something? 
P.S. As an extra offer, if you post the exact model number of the 10x 3TB disks, we can check that these are not SMR drives.
Well, I guess some sequences are more likely than others i.e. in the sequence presented in the BIOS.
The raid is most likely fine. Otherwise you wouldn’t see the pool and its single disk.
It’s just corrupted.
And it’s probably corrupted because it was a raid.
Maybe some more powerful zpool import commands can be used. Not sure that’s been attempted.
Start by trying zpool import -f as instructed.