The lib_size function returns the number of bytes used
by the data library, as stored on disk.
lib_size(x)The size of the data library in bytes as stored on the file system.
# Create temp directory
tmp <- tempdir()
# Create library
libname(dat, tmp)
# Add some data to library
lib_add(dat, mtcars)
lib_add(dat, iris)
# Check size of library
lib_size(dat)
# [1] 9757
# Clean up
lib_delete(dat)