May I ask whether Alfresco has 3000 nodes limitation? If I have 1 million files, I need to create 333 directories, each directory stores 3000 files? Do I need to care about this, I assume cloud storage API will cater this for us, I just put 1,000,000 files to Alfresco using Alfresco API, Alfresco will do the rest for us. I don't need to create 333 directories.
Alfresco is not a filesystem. Operations related to a large list of files involve complex SQL Queries and other heavy processes in the background. This is why a recommended maximum number of files per folder is around 3k-5k. In any case, the real number depends on your deployment and use of the platform.
Usually folder structure is used to apply a single criteria classification to files (like month or day), that helps to navigate the hierarchy and to avoid creating large collections of files under the same folder.
Alfresco has no limitation in the number of files that can be stored (there are deployments managing even billions of them), but with the recommended structure to get a better performance.