On Thu, Jan 15, 2015 at 9:53 AM, Cheng Cheng <ccheng.leo@xxxxxxxxx> wrote: > Hi Ceph, > > I am wondering is there a mechanism to prioritize the rbd_aio_write/rbd_aio_read I/Os? Currently all RBD I/Os are issued in FIFO to rados layer, and there is NO QoS mechanism to control the priority of these I/Os. > > A QoS mechanism will be beneficial when performing certain management operations, such as flatten. When flatten a image, the outstanding I/Os do get throttled by “rbd_concurrent_management_ops”. However this won't guarantee normal I/Os are not affected, as outstanding normal I/Os are still competing with concurrent management ops. > > Anyone know how/where to implement this QoS mechanism? Sadly, there's no QoS in RBD right now. It sounds like you're more concerned about preventing management from impacting client IO, but even in this case it's a distributed problem (flatten for instance involves moving data between storage machines), which is still an open research topic as far as I know. I don't think you'll ever be able to get a guarantee, and simply doing one movement at a time is probably as good as you can get in the medium term. :( -Greg -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
