Hi,
I suffered pretty much the same issue,and given this is first google hit thought would update solution for me here in case it helps others.
Exactly the same as here:
https://forum.netgate.com/topic/184135/mounting-failed-with-error-5/7
Pfsense Plus power cut (backup exhausted) bad shutdown.
Then failed to start.
Root mount waiting for: CAM (lots)
Then:
Mounting from zfs:Pfsense/ROOT/Default failed with error 5
Error 5, as per screen shots here.
Any zpool command gave error
“Invalid file system specification“
I pulled PC, pulled drive, booted from USB Pfsense stick.
Pulled hair.
Could not seem to get to bottom of.
Was going to reinstall Pfense (not plus) from USB stick - no drive to be found other than USB (?). Was going to replace drive altogether.
Then discovered one post, in a forum, somewhere, which I will link to if ever can find again, talking about BIOS drive settings changed in power cut.
Solution:
Somehow power surge/power cut had changed BIOS to RAID for drives from AHCI. (interestingly did so for another PC I discovered later - Pfsense was first job - this was Windows PC and failed to Boot altogether)
Oddly here though - Pfsense partially booted - as above so for drive was readable for parts…. (Hence hadn’t considered drive issue)
Solution:
Check BIOS Settings
Hard Drives - Selection - AHCI. (not RAID)
Hopefully this helps someone else in the future.