Hi Marty, On Tue, 23 Mar 2010 07:17:53 PDT, Marty Scholes <martyscholes at yahoo.com> wrote: > The speed limit of USB drives appears to be about 20 MB/s under > Opensolaris. > > My experience with 4 port PCI cards is that they have a single bridge and > some sort of internal hub, so the 20 MB/s speed limit is across all of the > ports, e.g. two drives connected to a 4 port PCI USB card will each produce > approx 10 MB/s throughput. >
A typical USB 2.0 chip composed of multiple USB 1.1 controllers and a single USB 2.0 controller with a set of ports. It is reasonable to think of the host controller as a hub. You can count the number of USB 2.0 controllers by looking at the "ehci" instances in prtconf -D. > Assuming I understand what is going on, does there exist a 4 port PCI card > which actually has four distinct pci-usb bridges? In other words, I am > looking for a card where each of the four ports can sustain the 20 MB/s > throughput. > > Right now, I am looking at adding PCI cards not for the ports, but for the > speed. The reason is that several USB drives serve as a USB backup pool > for the main array. > > Many thanks, > Marty http://en.wikipedia.org/wiki/Universal_Serial_Bus#USB_2.0_data_rates lists some existing chips which include multiple controllers and mentions that some of them are available on cards but I haven't seen any PCI or PCIe cards on the market... The 20M/s figure could reflect a device limitation rather a limit on the total bandwidth of the controller (although with the overhead for mass storage the ceiling is just above 40M/s, so you'd only be able to have two devices at that speed). -Albert
