When Xen Media Gallery wasn't part of XenForo this was somehow understandable but now that XFMG is part of XenForo I think this is totally unacceptable.
XFMG stores all the thumbnails that display inside the gallery within data/xengallery. The problem is that XenForo *stores another exact copy of every thumbnail* at data/attachments. This is a big problem for large galleries:
#du -h data/xengallery 2.6GB xengallery #find data/xengallery -type f | wc -l 41,052 files #du -h data/attachments 2.6GB attachments #find data/attachments -type f | wc -l 40,219 files
Again, this is unacceptable and should be addressed in the near future.