On 07/03/2014 05:46 PM, Greg Freemyer wrote:
One receiving disk maxes out at 108 Two receiving disks: Second drive takes advantage of first being maxed (not ready to receive) and it (#2) receives while #1 is busy. They take turns Agreed. but why don't I get better USB-3 bus utilization. A single drive does gets about 20% bus utilization. Why don't I get 40% with 2 drives?
By the time you have 5 targets, you've probably maxed out your sending disk and the wire is waiting for data. I'm not sure what you are saying. With "dc3dd wipe=/dev/sdb" all of the zeros come straight from the CPU. It can generate way more than 200MB/sec of zeros. The bottleneck is not the data source. It has to be the USB-3 bus.
There's a 'maybe' there. I think I mentioned that the old PDP-11 DMA disk controller -- I forget the model # - could support 8 drives but only one data channel, though it could do overlapped seeks. There was a parallelism that could be used by an astute programmer. I don't hear you telling us that you have low level control over the hub. I suspect that after you tell it to write to #1 and it returns busy so you now direct to #2 there is a negotiation overhead to switch to #2 and find that #2 is not busy. I'm not sure how much of this goes on in the linux lower level of the /dev/sdb drier and how much goes on in the hub; possibly both and some handshaking. But the issue is that this is too low level, unlike the PDP device where it is all exposed. I don't have any idea how you could verify or metricate this. -- /"\ \ / ASCII Ribbon Campaign X Against HTML Mail / \ -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org