On Oct 5, 2014, at 11:01 PM, lars hofhansl <la...@apache.org> wrote:
>>> - rack IO throttle. We should add that to accommodate for over subscription >>> at the ToR level. >> Can you decipher that, Lars? > > ToR is "Top of Rack" switch. Over subscription means that a ToR switch > usually does not have enough bandwidth to serve traffic in and out of rack at > full speed. > For example if you had 40 machines in a rack with 1ge links each, and the ToR > switch has a 10ge uplink, you'd say the ToR switch is 4 to 1 over subsctribed. > > > Was just trying to say: "Yeah, we need that" :) > Hmmm. Rough math… using 3.5” SATA II (7200 RPM) drives … 4 drives would max out 1GbE. So then a server with 12 drives would max out 3Gb/S. Assuming 3.5” drives. 2.5” drives and SATAIII would push this up. So in theory you could get 5Gb/S or more from a node. 16 serves per rack… (again YMMV based on power, heat, etc … ) thats 48Gb/S and up. If you had 20 servers and they had smaller (2.5” drives) 5Gb/S x 20 = 100Gb/S. So what’s the width of the fabric? (YMMV based on ToR) I don’t know why you’d want to ‘throttle’ because the limits of the ToR would throttle you already. Of course I’m assuming that you’re running a M/R job that’s going full bore. Are you seeing this? I would imagine that you’d have a long running job maxing out the I/O and seeing a jump in wait CPU over time. And what’s the core to spindle ratio?