I have copie the metadata file and my two most important columns are like this :
<meta name="calibre:user_metadata:
#type_of_book" content="{link_column: value, is_multiple: null, rec_index: 25, is_custom: true, is_category: true, label: type_of_book, is_editable: true, table: custom_column_2, colnum: 2, name: Type of book, datatype: text, #value#: bd, column: value, search_terms: [#type_of_book], kind: field, display: {use_decorations: 0, description: }, category_sort: value, is_csp: false, #extra#: null, is_multiple2: {}}"/>
<meta name="calibre:user_metadata:
#classification" content="{link_column: value, is_multiple: null, rec_index: 22, is_custom: true, is_category: true, label: classification, is_editable: true, table: custom_column_3, colnum: 3, name: Classification, datatype: text, #value#: Humour, column: value, search_terms: [#classification], kind: field, display: {use_decorations: 0, description: }, category_sort: value, is_csp: false, #extra#: null, is_multiple2: {}}"/>
IN order to create a new library, I will need to add the above 2 custom columm. beyond the name which I underlined and the fact that these are text field what else do I need to use in the definition ?
I separated the book folder (150 gb) which I stored on my 1 tera hard disk from the structure and other files which I did not even notice were put on my SSD by Calibre under my user name. is this the answer to your question. I know in the future I will keep a copy of that, I did not realize
I did not have an image either before reinstalling windows (another lesson).
Thanks