On Thu, Oct 9, 2014 at 6:31 AM, Jean-Marc Spaggiari <[email protected] > wrote:
> For #4, one more thing me might want to add is a safety valve to increase > throttle in case compaction queue become bigger than a certain value? > > JM > > Would that make resolution of the problem leading to a large queue in the first place more difficult do you think? > 2014-10-09 1:20 GMT-04:00 lars hofhansl <[email protected]>: > > > Hi Michael, > > > > your math is right. > > > > > > I think the issue is that it actually is easy to max out the ToR switch > > (and hence starve out other traffic), so we might want to protect the ToR > > switch from prolonged heavy compaction traffic in order to keep some of > the > > bandwidth free for other traffic. > > Vladimir issues were around slowing other traffic while compactions are > > running. > > > > > > -- Lars > > > > > > > > ----- Original Message ----- > > From: Michael Segel <[email protected]> > > To: [email protected]; lars hofhansl <[email protected]> > > Cc: Vladimir Rodionov <[email protected]> > > Sent: Wednesday, October 8, 2014 12:30 PM > > Subject: Re: Compactions nice to have features > > > > > > > > On Oct 5, 2014, at 11:01 PM, lars hofhansl <[email protected]> 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? > > > -- Best regards, - Andy Problems worthy of attack prove their worth by hitting back. - Piet Hein (via Tom White)
