On Sun, Jan 04, 2009 at 04:55:18AM -0500, Justin Piszcz wrote: >> The biggest different for RAID is what happens when multiple >> channels are used. On full speed streaming read/write almost >> every (even the worst PCI controllers on a PCI bus) sata >> controller is close to equal when you only have one drive, once >> you use 2 drives or more things change. If the given controller >> setup can actually run several drives at close to full single >> drive speed performance will be good, if it cannot things are >> going to get much slower. So, in general, the ideal is to be able to simultaneously read/write from multiple disks at the same speed as a single drive. > This has been discussed before, on the southbridge it is usually > good/you will get the maximum bandwidth for each of the 6 sata > ports. After that, you need to use PCI-e lanes from the > northbridge. Using PCI-e x1 slots that come off the southbridge > can degrade performance of the 6 SATA ports or the speed coming > off the drives connected to the x1 slots will be slow. Are you talking about using additional SATA controllers (i.e. via add-on cards)? Or simply talking about the interconnect between the southbridge and the northbridge? I think you're talking about the former, i.e. the SATA controller integrated in the southbridge generally ought to be fine, but if you start adding additional controllers that hang off the south bridge, their could be competition for bandwidth to the northbridge... right? (And wouldn't the nvidia chips have an edge here, since they have everything combined into one chip?) Makes intuitive sense anyway; but in my case I'm really just curious about the SATA controller integrated into the southbridge; not concerned with additional SATA controllers. > What are you trying to accomplish? Trying to determine what motherboard would be ideal for a home NAS box AND have the lowest power consumption... the AMD solutions seem to win on the power consumption front, but I'm not sure about the performance. > As Roger pointed out, doing a dd is a good way to test, from each > disk, simultaneously, on an old Intel P965 board I was able to > achieve 1.0-1.1Gbyte/sec doing that with 12 Velociraptors and > 1.0Gbyte/sec reads on the XFS filesystem when dd (reading) large > data on the volume. Approx 500-600MiB/s from the southbridge, the > other 400MiB/s from the northbridge. Is the "parallel dd test" valid if I do a raw read off the device, e.g. "dd if=/dev/sda of=/dev/null"? All my drives are already in an md array, so I can't access them individually at the filesystem level. Thanks for the feedback and info! Matt -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
