Thrashing the system buffer when deleting LVM volume

[lirenke]

When cinder begin to delete LVM volume, "dd" command would be called, then clear content and remove volume.

During clear volume, cinder check whether O_DIRECT is supported, and the below command be called:

"dd count=0 if=/dev/zero of=/dev/VG/volume-*** iflag=direct oflag=direct"

But this command never be executed successfully because of "/dev/zero" and "iflag=direct".
So the extra_flags will be reset and the below cammand is :

"dd if=/dev/zero of=/dev/VG/volume-*** count=*** bs=* conv=fdatasync"

The O_DIRECT flag lose. It may trash system buffer and make system unstable.

[Jay Bryant (jsbryant)]

This is an issue that has been discussed several times before. At the moment the following solution was implemented: https://blueprints.launchpad.net/cinder/+spec/when-deleting-volume-dd-performance -- https://review.openstack.org/74810

So, ionice is the method provided to reduce consuming the system's resources when doing the DD. I believe the reason that O_DIRECT is not being used for the following reason: http://osdir.com/ml/ubuntu-bugs/2012-11/msg24054.html

Do you have a way to make sure that we don't have issues with O_DIRECT on ubuntu?

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tomoki Sekiyama (<email address hidden>) on branch: master
Review: https://review.openstack.org/91849
Reason: This problem has been fixed by commit I4b627e95b68d56e3011cddc577c62fad0c384dba.

[Tomoki Sekiyama (tsekiyama)]

Fixed by commit I4b627e95b68d56e3011cddc577c62fad0c384dba (Review: https://review.openstack.org/#/c/93461/ )