关于Qcow2特性的一些总结

One important feature of 'qcow2' is the 'Copy-on-Write' images. 

  • The "cow" part of qcow2 is an acronym for copy on write, a neat little trick that allows you to set up an image once and use it many times without changing it. This is ideal for developing and testing software, which generally requires a known stable environment to start off with. You can create your known stable environment in one image, and then create several disposable copy-on-write images to work in.
  • To start a new disposable environment based on a known good image, invoke the qemu-img command with the **backing_file** option and tell it what image to base its copy on. When you run QEMU using the disposable environment, all writes to the virtual disc will go to this disposable image, not the base copy.
And some advice follows: 
  • don't forget to copy any important data out of the disposable environment before deleting it. When developing and testing software in copy-on-write virtual environments, it is a good idea to use version control software like Subversion or CVS on a server external to your virtual environment. Not only is it easy to keep copies of your work outside your virtual environment, it is also very easy to set up a new virtual environment from version control. 
  • backing\_file image must be set as **read-only** on VMs, that will be using it directly. Otherwise, other images, based on this backing\_file image will be **corrupted**, if there is some change have been made to the backing_file image

When design something to store the different images, this feature can decrease the storage due to the 'cow' of qcow2 image. 
According to the advice. Use a version control software can help us easliy keep the copies of images referring to the same backing_file.

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