On Wed, Jul 02, 2008 at 01:08:04PM -0500, David Lethe wrote: > > > And also the disk controllers, could these be bottlenecks? They typically > operate at 300 MB/s nominally, per disk channel, and presumably they > then have a connection to the southbridge that is capable of handling > this speed. So for a 4-disk SATA-II controller this would be at least > 1200 MB/s or about 10 gigabit. > > best regards > keld > ------------------- > It is much more complicated than just saying what the transfer rates are, especially in the world of blocking, arbitration, and unbalanced I/O. Yes, that is understood, but I am only listing some potential bottlenecs, of cause there may be more. > Everything is a potential bottleneck. As I am under NDA with most of the controller vendors, then I can not provide specifics, but suffice to say that certain cards with certain chipsets will max out at well under published speeds. Heck, you could attach solid-state disks with random I/O access time in the nanosecond range and still only get 150MB/sec out of certain controllers, even on a PCIe X 16 bus. > > BTW, there isn't a SATA-II controller in the planet that will deliver 1200 MB/sec with 4 disk drives. Yes, but I think this is normally due to that the max transfer speed per disk is in the ballpark of 80-120 MB/s - which is less than half the SATA-II max speed. And I think much of this slowdown comes from head movement, track-to-track, disk latency etc. I was of the impression, that when the transfer between the disk and the controller is going on, then the transfer speed would be not far from the 300 MB/s max speed, eg for 90 MB/s 1 TB disks that I bougth recently, or the faster 15000 RPM disks, which give something like 120 MB/s. 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
