Let's try to clear up the confusion. Kernel device-mapper (which lvm uses) does not support write barriers except in very restricted circumstances (when only one device is involved and the mapping is trivial). If dm receives a write barrier which is not supported it notifies the caller (typically a filesystem) so appropriate action can be taken if it wishes. Several kernels releases ago, the implementation of the 'flush device' operation in the block layer was changed from a simple function call that dm supported to a mechanism involving barriers that is trickier for dm to support. Previously 'flush' could not fail and so callers do not generally have strategies to handle such a situation. The latest of several attempts to support barriers is contained in patches here: http://patchwork.kernel.org/project/dm-devel/list/?q=barriers Please review and test if you are interested! Alasdair -- agk@redhat.com _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
