[itimpi]

I can tell you from experience that Calibre does NOT clear out the library folder if there are files in there it does not have in its metadata database.

When Calibre is about to delete any files it has a confirmation dialog before it proceeds, so again it seems unlikely it can go mad deleting files.

I guess a lot depends on what caused the orignal error. If it was at the file-system level it could have been Windows that deleted all the files!

Having said that, I do back up the Calibre database and associated files at regular intervals as a lot of effort has gone into organising my collection and getting all the metadata and cover art as I want them, let alone the conversions into formats suitable for my e-book readers.