Why StorageFolder.CreateFileAsync(String) creates file fail without any exception thrown?

I need to develop a windows phone store app to test file system. And I use StorageFolder.CreateFileAsync to create a file on ApplicationData.Current.LocalFolder path and write1MB text content, and read it, modify it, and re-write it. But after about 5000 times write/read.I found that the applicaition blocked at StorageFolder.CreateFileAsync through a test method of log. However, there isn't any exception thrown. Why did the StorageFolder.CreateFileAsync  fail? And how to solve this problem? We need to write/read about 150000 times.