为什么Docker vfs存储后端不适合生产？

Docker vfs存储后端在几个地方被提及为不是生产后端(参见Michael Crosby的这个Docker GitHub issue comment).是什么让它不适合生产？

Project Atomic的description of storage backends说：

The vfs backend is a very simple fallback that has no copy-on-write support. Each layer is just a separate directory. Creating a new layer based on another layer is done by making a deep copy of the base layer into a new directory.

Since this backend doesn’t share diskspace use between layers,and since creating a new layer is a slow operation this is not a very practical backend. However,it still has its uses,for instance to verify other backends against,or if you need a super robust (if slow) backend that works everywhere.

根据该描述,听起来唯一的缺点是可能会使用更多磁盘空间并且创建图层可能会更慢.但是在运行时访问文件时没有提到缺点,它甚至被描述为“健壮”.单独的磁盘空间问题似乎不是生产使用的阻止程序.