I have a few questions on multiple libraries v virtual libraries that I would appreciate any input on. I know there are many different opinions and preferences but I’m interested to know why you choose to manage your library a certain way etc…
I use both multiple libraries and virtual libraries, although thinking of really only using multiple libraries. I don't need to search between the different libraries. I'm probably not using virtual libraries to their fullest potential, but I can look at that later.
1. Do you use multiple libraries or/and virtual libraries?
Both
2. How do you use multiple libraries or/and virtual libraries?
Multiple libraries - Do you use them to manage different types of libraries? I.e Books, Comics, Manuals, Journals etc...
Yes - Books, Journals, Media, Comics physical libraries - because my custom column requirement for each are quite different. I want to avoid the trap of overloading columns with different usages depending on publication type
or for different reasons - To review etc...
Physical libraries for Intake, Duplicates, Test
Virtual libraries - How do you use virtual libraries? Why? List some examples.
Varies for each library - but primarily administrative and few in number.
The manual lists the following examples.
Books added to calibre in the last day:: date:>1daysago
Books added to calibre in the last month:: date:>30daysago
Books with a rating of 5 stars:: rating:5
Books with a rating of at least 4 stars:: rating:>=4
Books with no rating:: rating:false
Periodicals downloaded by the Fetch News function in calibre:: tags:=News and author:=calibre
Books with no tags:: tags:false
Books with no covers:: cover:false
Nothing like any of the above - mine are atypical, and often transient - i.e. project related
3. What are the strengths and weaknesses of using multiple libraries or virtual libraries?
- Do the multiple libraries run faster if there are less books in each library compared to having all the books in the one virtual library?
No significant performance difference between my Books library of 3,500 books and my Journals library of 150,000 books
- How easy is it to change from multiple libraries to one library with virtual libraries and vice versa?
Disparate custom columns would make it hard for me to merge my 4 main libraries into one - besides as I imagine Jane Seymour might have have said - Why would I want to do that 
I did split Comics out of my Media library recently. That was easy I just took all the custom columns from Media to Comics with Copy to Library, and then culled the columns I didn't want and added the columns I did want. Which reinforces my notion that the main reason for having different physical libraries is because of the need for different custom columns for different ''publication types'.
- My library is only fairly small (1500) compared to what I have heard some other Calibre users have (10,000 +). As people are reading more ebooks, it is easier to collect a large quantity of books and keep them, however this means trying to find certain books and managing them can be even harder. For the people with really big libraries, do you prefer to use multiple libraries or a virtual library to manage your books?
I don't regard Real and Virtual libraries as either/or alternatives
Multiple libraries
Strengths
- You prefer to display certain columns for each of your libraries
Yes, but that's something I do via the View Manager plugin - all of my libraries (except Test) have a set of stable View Manager column layouts and sort orders
Weaknesses
- You cannot search through multiple separate libraries simultaneously in calibre.
I don't do many searches in calibre - I do far more full text content searches (which usually result in creating/maintaining Reading Lists) than calibre metadata searches
- You can only view view/upload one library to Calibre Companion (CC)
Don't use CC
I only keep a few books on a tablet and/or a phone, which I manage myself
Virtual libraries
Strengths
- Preferred way of splitting up your library when you want to search through your entire collection
Irrelevant to me
- It will restrict the list of books shown in a book list but it will also restrict the entries shown in the tag browser
True - if I go to a branch bricks and mortar library I can't easily see what's on the shelves of the main library 10km away. There, I would fossick through the library's catalogue - with calibre I would do the same via the CalibreSpy plugin.
- You can view your entire library in Calibre Companion (CC) using virtual libraries.
True - but that's irrelevant to me
Sorry...lots of questions...but very keen to hear everyone’s thoughts.
Inukami