On Tue, Jul 27, 2010 at 07:54:19PM +0200, Jan Kara wrote: > OK, let me understand one thing. So the storage arrays have some caches > and queues of requests and QUEUE_ORDERED_DRAIN forces them flush all this > to the platter, right? Not quite. QUEUE_ORDERED_DRAIN does not interact with the target at all, it's entirely initiator (Linux) side. What it does it to make sure we drain the whole queue in the I/O scheduler (elevator) and in flight to the device (command queueing) by waiting for all I/O before the barrier to finish, the issue the barrier command and only then allow any newly arriving requests to proceed. > So can it happen that they somehow lose the requests that were already > issued to them (e.g. because of power failure)? We can lose the requests already on the wire, but not completed yet. That's why log write wait for all preceding log writes (or things like the I/Os required to push the tail) and fsync waits for all I/O completions manually. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
