> First of all, I've yet to see a controller that is really able > to handle multiple requests in parallel. Usually, multiple > I/O threads gets exactly the same summary performance as a > single thread - UNLIKE of linux software raid which clearly Thats usually true of hardware raid cards as they lack enough CPU power and they are on a single PCI slot. With PCIE and things like AHCI where the host is doing the hard work and the controller engine is doing the NCQ low level work and channel work you've got a much better chance. > They says that modern SATA drives has NCQ, which is "more > advanced" than ol'good TCQ used in SCSI (and SAS) drives. > I've no idea what's "advanced" in it, except of that it > just does not work. There's almost no difference with > NCQ turned on or off, and in many cases turning NCQ ON > actually REDUCES performance. NCQ is straight 32 way tagged queueing. On some workloads it makes a big difference but its dependent on controller and drive firmware. The big big constraint on a modern drive is still ops/second. Its mechanical and the mechanical behaviour is limited by the laws of physics and hasn't much changed in years If you want really high performance use multiple drives, on multiple PCIE controllers. Just make sure your backup planning of raid 1+0 setup is done right as many drives means a lot more drive fails. - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
