Where does Longhorn store inode tables for ext4 volumes?

[ncecsc]

I recently had a longhorn drive go into a "Faulted" condition and needed to recover the data stored on it.
Not knowing how to recover this data using Longhorn tools (Salvage didn't work), we tried recovering the data by mounting the .img file, but testdisk said the inode table was missing.

We managed to recover the data using fsck and photorec, but it left me wondering where the inode table for volumes actually lives?
Is it stored in a cache separate from the volumes, or is it usually there and my volume was just horribly corrupted somehow?