The inability to monitor block I/O statistics via iostat for device-mapper mapped devices seems like a big loss. Are there plans to provide this feature? Seems like being able to initiate i/o requests to device-mapper target devices from within a device-mapper target driver is a missing link in the device-mapper architecture. Are there plans to provide this feature? Since the multipath hardware context code for the CLARiion places path priority group initialization I/O requests directly on its target device queues it must be the case the CLARiion target devices must be ones which have a request_fn_proc() queue service function -- which rules out using other device-mapper mapped devices or md devices as target devices. This restriction appears not to be in place for other storage systems supported by multipath.
