I am using LR 6 and recently moved my photos and catalogue to an external hard drive. I thought (foolishly) that all had gone well but now I see that many (but not all) of the thumbnails in the Library view have a downward pointing arrow in the upper right hand corner which, I understand, indicates that the metadata needs to be updated. When I do update an individual photo the only thing that changes is the Metadata date is updated to the current date. Is there a way to update all of the files at the same time? I found an earlier post that suggested selecting all of the photos and using "save metadata" but once I select all of the photos the "save metadata" command is grayed out. Is this issue symptomatic of a more serious condition that I caused by moving the files and catalogue to an external drive?