resize revert will let new data lost!

[tony]

* description:
      Hi all，I found a serious problem in revert resize action for a vm. the revert resize operation will let the increments data lost. the reproduction steps show below.

* Step-by-step reproduction steps:
1、 create a new vm， which flavor choice C1-R2-D10（Core：1， Ram： 2G， Disk：10）， image：centos 76

2、login the vm, and touch a new file: 1.txt, and write some message to the file. like: echo 'aaa' > 1.txt

3、do resize operation for the vm. change flavor to C2-R4-D20. but do not confirm or revert the operation now.

4、login the vm again, and touch another new file: 2.txt, and write some message to the file. like: echo 'bbb' > 2.txt

5、now we do revert-resize operation, revert the resize operation which in 2 step.

6、when the revert resize done, login in the vm, and we will found the 2.txt will lost.

* Expected output:

    I think the increment 2.txt added between do resize and revert should be preserved.

* Actual output:

     but the 2.txt lost ！！

* Version:
  ** OpenStack version： Rocky
  ** Linux distro, kernel. CentOS Linux release 7.8.2003 (Core)、3.10.0-1127.el7.x86_64

[Slawek Kaplonski (slaweq)]

I don't know how this can be neutron bug really. I will move it to Nova for now.

[tony (yanhongchang5)]

Hi Slawek Kaplonski,

   Am I reported the bugs to neutron project ? I am so sorry， it's my fault. Actually, In fact, In the beginning I wanted report the bugs to nova project。 Thank you for your attention Slawek

[Stephen Finucane (stephenfinucane)]

I assume you're referring to instances with ephemeral or local storage? If so, this is expected behaviour. Resize revert deletes the instance on the destination host and resumes the old instance on the source host. You can work around this by using boot from volume or RBD.

[tony (yanhongchang5)]

Thank you for your attention, Stephen.

    yes, The VM I boot by the way of boot from image. but in my opinion, even if the user do the revert resize operation, the data changes between the operation of resize and revert should not lost， because the VM still provides services and still has possibility of data changes between the two operation. so I think the problem should be consider more.