On Sun, Jan 04, 2009 at 04:32:27PM -0500, Justin Piszcz wrote: > > > On Sun, 4 Jan 2009, Matt Garman wrote: > > >On Sun, Jan 04, 2009 at 04:55:18AM -0500, Justin Piszcz wrote: > > > >>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. > How fast do you need? Gigabit is only ~100MiB/s. Are you buying a 10Gbps > card? My impression is that using on-mobo sata controllers gives you adequate bandwidth. SATA-controllers with 20 Gbit/s - or 2,5 GB/s bidirectional speeds are more than adequate for say 4 disks of 80 - 120 MB/s speed. And anyway, if you run in a multiprocess environment the random access read or write speed per disk is normally only about half of the sequential speed. I have a mobo with 2 SATA controllers with 4 ports each, with my GB disks, it can generate max 700 MB/s which is much less than the 2,5 GB/s that the southbridge can deliver. Using 1 Gbit/s ethernet connections may easily become a bottleneck. We do have a bottleneck section on our wiki: http://linux-raid.osdl.org/index.php/Performance#Bottlenecks > >>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. > Yes. You do not need to access them at the filesystem level. Both RAW > and on the filesystem, my benchmarks were the same when reading from 10 > disks > raw or reading in a large file with dd using XFS as the filesystem. My impression is different, it does matter for certain raid types in a parallel dd test whether you run it off the raw devices or off a file system. At least if you dd different files in parallel off the same device. best regards keld -- 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
