`storage.File` uses a single file to store all records.
Writes using `Set(key, value)` are async and only mark the collection as "dirty" which is very quick.
The sync to disk happens shortly afterwards.
Every collection uses one goroutine to check the "dirty" flag, write the new contents to disk and reset the flag.
The biggest advantage of `storage.File` is that it scales well with the number of requests:
Suppose `n` is the number of write requests and `io` is the time it takes for one write. Immediate storage would require `O(n * io)` time to complete all writes but the async behavior makes it `O(n)`.
You should use `storage.File` if you have a permanently running process such as a web server where end users expect quick responses and background work can happen after the user request has already been dealt with.
Make sure you `defer collection.Sync()` to ensure that queued writes will be handled when the process ends.