When a drive fails, it's likely to have been some time since the administrator configured the system. The admin may not even remember if the drive was encrypted or if it has an (optional) passphrase.
Sections 9.5.1 and 184.108.40.206 of the 11.2-U7 UG cover this topic. Early on, 9.5.1 says, "If the pool is encrypted with GELI, refer to Replacing and Encrypted Disk before proceeding." But if the admin does not know if the disk is encrypted or not, it does not explain how to find out.
Apparently the GUI does not provide this information. If it does, then 9.5.1 and 220.127.116.11 ought to explain how to access it. Otherwise, I suggest adding this feature to the GUI.
In my case, I found this forum post and was able to determine my pool is indeed encrypted. I suppose another, less reliable, way would be to look around for a saved GELI encryption key. But improved documentation from IX, ane perhaps an easier way to retrieve the information from the GUI would be much appreciated.
Similar issues arise with the passphrase, but in this case the solution is easier. Since a passphrase is optional, the first issue is to determine if one was set. Section 9.2.2 explains that Storage / Pools / Create Passpharase chages to Storage / Pools / Change Passphrase. So if 18.104.22.168 even gave a hint of this, the user could learn how to determine if there's a passphrase or not. But rather than make the user read all of 9.2.2, I'd prefer 22.214.171.124 to summarize what the user needs to do:
"To determine if you have a passphrase, choose Storage > Pools, and click on the lock icon on the right. If the menu that appears includes 'Create Passphrase,' currently there is none. If it includes 'Change Passphrase,' then one already exists."