We've been working for a couple of weeks now to implement an XFS recovery capability for our ReclaiMe data recovery software. The single most significant impression is that XFS is unnecessarily and exceedingly complex. Having... how many that would be, five? types of directories is actually OK, as long as these types utilize the same basic structures and design. Taking design commonalities into account, the number of distinct directory types is reduced to just two. Data storage comes in three forms (NTFS and ext4 are both OK having just two). The most interesting discovery of all to date was that each allocation group has two different sizes.