On Wed, May 30 2007, Phillip Susi wrote: > >That would be the exactly how I understand Documentation/block/barrier.txt: > > > >"In other words, I/O barrier requests have the following two properties. > >1. Request ordering > >... > >2. Forced flushing to physical medium" > > > >"So, I/O barriers need to guarantee that requests actually get written > >to non-volatile medium in order." > > I think you misinterpret this, and it probably could be worded a bit > better. The barrier request is about constraining the order. The > forced flushing is one means to implement that constraint. The other > alternative mentioned there is to use ordered tags. The key part there > is "requests actually get written to non-volatile medium _in order_", > not "before the request completes", which would be synchronous IO. No Stephan is right, the barrier is both an ordering and integrity constraint. If a driver completes a barrier request before that request and previously submitted requests are on STABLE storage, then it violates that principle. Look at the code and the various ordering options. -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
