此为本人按照苹果英文文档翻译。可英汉对照来看，欢迎提宝贵意见。
官方地址https://developer.apple.com/icloud/documentation/data-storage/index.html
To ensure that backups are as efficient as possible, store your app’s data according to the following guidelines:
为了确保尽可能高效的备份,请根据以下指南存储你的应用程序数据:
Only documents and other data that is user-generated, or that cannot otherwise be recreated by your application, should be stored in the <Application_Home>/Documents directory and will be automatically backed up by iCloud.
只有用户生成的文件和数据,或,否则不能被重新创建应用程序数据,应该存储在< Application_Home > /Documents 目录下并将通过iCloud自动备份这些文件。
Data that can be downloaded again or regenerated should be stored in the <Application_Home>/Library/Caches directory. Examples of files you should put in the Caches directory include database cache files and downloadable content, such as that used by magazine, newspaper, and map applications.
一些可以被下载的，或者可以再次自动产生的数据,应该存储在< Application_Home > /Library/Caches目录下。可以放在缓存目录下的内容包括数据缓存，下载内容。如杂志、报纸、地图应用程序。
Data that is used only temporarily should be stored in the <Application_Home>/tmp directory. Although these files are not backed up to iCloud, remember to delete those files when you are done with them so that they do not continue to consume space on the user’s device.
一些临时的数据应该存储在< Application_Home > / tmp目录下。尽管这些文件没有通过iCloud备份。记得要删除这些文件当你用过他们后,使他们不继续消费用户设备上的存储空间。
Use the "do not back up" attribute for specifying files that should remain on device, even in low storage situations. Use this attribute with data that can be recreated but needs to persist even in low storage situations for proper functioning of your app or because customers expect it to be available during offline use. This attribute works on marked files regardless of what directory they are in, including the Documents directory. These files will not be purged and will not be included in the user's iCloud or iTunes backup. Because these files do use on-device storage space, your app is responsible for monitoring and purging these files periodically.
使用“do not back up”属性指定文件保存在设备上,即使在存储不足的情况下。使用这个属性可以使可再生数据在存储空间不足的情况下仍然被保存,以便应用的一些特有功能，或者用户想离线使用的功能来读取这些数据。被这个属性处理过的文件，无论他在那个目录文件下，包括Documents 文档目录。这些文件都不要会被清除，不会通过iCloud或者iTunes备份。这些文件占用的设备存储空间，由你自己的应用负责定期监控和清理。
可以采用方法防治iCloud备份，此为官方技术文档。https://developer.apple.com/library/ios/qa/qa1719/_index.html