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From: | Stefan Weil |
Subject: | Re: [Qemu-devel] -snapshot |
Date: | Thu, 16 Dec 2010 19:16:16 +0100 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101030 Iceowl/1.0b1 Icedove/3.0.10 |
Am 16.12.2010 18:45, schrieb Stefan Hajnoczi:
On Thu, Dec 16, 2010 at 4:34 PM, Amador Pahim <address@hidden> wrote:Thank you for your answer. Just one more question: If, while my "snapshot" vms are running, the main disk is modified by a non "snapshot" vm? For example, installing some extra software.. this can freeze vms or something?Correct, it is not safe to modify the base image while there is another disk image backed off it. The reason for this is that the image only needs to store the changes that were made on top of the base image. For anything which hasn't been modified it will go back to the base image and read data from there. If you modify the base image, then the filesystem in the base image is not longer what your image file was created from and you have an inconsistent view of the disk. It leads to odd behavior and is unsafe. Stefan
There are useful scenarios where using the same disk simultaneously from a snapshot vm and a real system works. If you have a hard disk with a dual boot configuration, it is sometimes useful to boot one configuration with the real system, then start qemu and boot the second configuration. Even booting the same configuration twice (once with the real machine, once with qemu snapshot) is sometimes useful and works to a limited degree. It is a simple way to try new bootloader configurations or other boot setups. Regards Stefan
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