Ehcache - restore from disk upon startup

Question

I am using Ehcache 3.10. I am using persistent cache, configured as follows:

   PersistentCacheManager persistentCacheManager = CacheManagerBuilder.newCacheManagerBuilder()
            .with(CacheManagerBuilder.persistence("\ + File.separator + "squaredValue"))
            .withCache("persistent-cache",
                        CacheConfigurationBuilder.newCacheConfigurationBuilder(Integer.class, Integer.class,
                                                ResourcePoolsBuilder.newResourcePoolsBuilder()
                                                                    .heap(10, EntryUnit.ENTRIES)
                                                                    .disk(10, MemoryUnit.MB, true)))
            .build(true);

    Cache<Integer, Integer> squareNumberCache = persistentCacheManager.createCache(
        "squaredNumber",
        CacheConfigurationBuilder.newCacheConfigurationBuilder(Integer.class,
                                                               Integer.class,
                                                               ResourcePoolsBuilder.heap(10)));

Based on file size, it seems the cache is getting persisted to disk. I have a few questions:

1. I am assuming the config is setting up a two tier cache - Heap and Disk. Is my understanding correct?
2. When does data from the Heap get persisted to the disk? Or is that always happening?
3. Is there a way I can control when data gets persisted to disk? (As a way to improve performance by lowering the write to disk.)
4. When the app restarts, the cache does not seem to be hydrated from the disk. Can someone please share sample config / startup code to load the data in disk to cache.

Thank you in advance, Ahmed.