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Locating bottleneck on my LAN

Last response: in Networking
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August 17, 2012 12:34:37 AM

PROBLEM: My main machine will only transfer data at 4.5MB/s or so despite the fact it has a Gigabit NIC.

MY SETUP: I assume we can disregard other machines on the home network. Let me know if I am wrong about that.

Desktop - intel E5400 6GB ram / Gigabit NIC
Router - Linksys/cisco E3000 loaded with Tomato firmware 1.28(I think)
USB hard drive - connected to router - USB 2.0 compliant - 2TB seagate external
Cat5e cable thoughout


So, when I copy large files from my desktop to this USB hard disk I am only getting less than 5MB/s transfer rate. This mystifies me. I believe the theoretical weakest link would be the USB 2.0 bus speed of roughly 25MB/s right?

So how do I locate the problem?

Thanks in advance!
August 17, 2012 12:54:40 AM

Actually USB 2.0 should theoretically deliver up to 60MBps (480Mbps). The problem here is the assumption on your part that the router can drive the data any faster than 25MBps. Routers are relatively marginal devices, with modest processors and small amounts of memory. And so in this case, the weakest link is probably not USB 2.0, but the router itself! You see this same problem with low-end/budget standalone NAS devices (e.g., D-Link DNS-321) where they’ll provide Gigabit support, but routinely top out at 12-15MBps (so your router is actually even a little better).
August 17, 2012 10:03:48 AM

eibgrad said:
Actually USB 2.0 should theoretically deliver up to 60MBps (480Mbps). The problem here is the assumption on your part that the router can drive the data any faster than 25MBps. Routers are relatively marginal devices, with modest processors and small amounts of memory. And so in this case, the weakest link is probably not USB 2.0, but the router itself! You see this same problem with low-end/budget standalone NAS devices (e.g., D-Link DNS-321) where they’ll provide Gigabit support, but routinely top out at 12-15MBps (so your router is actually even a little better).


Well that just plain flat out sucks. :cry: 

I thought you were going to say something like "oh, thats because you have to change setting x on your router, then you'll be all set". <sigh>

What you said makes complete sense though. Much like having a NAS with slow hard disks, chalk this up to a cheap router. So what's the solution? A commercial grade router?

Also, I'm not getting 25MBps, its typically < 5MBps.

Thanks again!
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Best solution

August 17, 2012 1:31:06 PM
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The best solution is to get a *real* NAS. These router-based solutions are a cute and clever way to add NAS capability on the cheap. And good enough for light duty and modest needs. But they're not serious solutions if you want/need real performance.

When it comes to NAS and performance, it's a relatively straight line between performance and cost. If you want something much closer to Gigabit speeds, and your HDs have the capability, then you need to consider more serious equipment. I suggest looking through the Tom’s Hardware NAS performance charts.

http://www.tomshardware.com/charts/nas-raid-storage,58....

August 26, 2012 2:38:34 PM

Best answer selected by moveright.
August 26, 2012 2:39:57 PM

Thank you very much. I appreciate it!

<sigh> Everything has to be complicated. Quick question though... If I had a real NAS, wouldnt it be going through my router as well? Wouldn't that slow it down and negate its purpose?

August 26, 2012 3:03:00 PM

Depends on the router. If the router is only 10/100Mbps (which is by far the norm), and your NAS is capable of Gigabit speeds, then obviously you wouldn't want to route access through the router's switch. Instead, you'd want to hang a Gigabit switch off the router's switch and attach all your Gigabit devices to the Gigabit switch, leaving the router's switch for 10/100Mbps devices and internet access. Notice too, if the router's wireless AP is capable of more than 100Mbps, it’s STUCK on the router’s 10/100Mbps switch!

So it gets even more complicated. :) 

August 26, 2012 3:14:52 PM

eibgrad said:
Depends on the router. If the router is only 10/100Mbps (which is by far the norm), and your NAS is capable of Gigabit speeds, then obviously you wouldn't want to route access through the router's switch. Instead, you'd want to hang a Gigabit switch off the router's switch and attach all your Gigabit devices to the Gigabit switch, leaving the router's switch for 10/100Mbps devices and internet access. Notice too, if the router's wireless AP is capable of more than 100Mbps, it’s STUCK on the router’s 10/100Mbps switch!

So it gets even more complicated. :) 


hmmm.... Well, my router is a Linksys E3000 which is 10/100/1000. But, if I am understanding your second response in this thread, the problem is that the router's hardware is not beefy enough to push data at this speed. So, wouldn't that mean that no matter what was at either ends of this router (be it a serious NAS, powerful PC or, weakly powered PC) , due to its hardware insufficiencies, data transfer at that speed would simply not be attainable?

It really is pitiful actually, I copied a movie .mkv from my main desktop machine (gigabit NIC) to my USB 2.0 hard disk attached to my router last night and the highest noted transfer speed was 2.10MBps. Almost 3GB file took 25 minutes to transfer. I figured that router was decent, I didn't know there were routers available that had very powerful internals.

This sucks. I was considering building a small Linux tower out of an old Dimension 2400 (well 2350 to be exact but it has the intel P4 and not the celeron). I was going to make that my file server, set it up with a boatload of storage and a gigabit NIC. I suppose that would be effectively pointless and NOT a resolution to a possible improvement?
August 26, 2012 4:31:40 PM

When I said the router wasn't "beefy enough" (to use your words), I meant in terms of being able to process data from the HD drive off the USB port. So it's not the switch that's the problem. The switch is only there as a convenience and doesn't really come much into play at all. In fact, some routers actually use a separate chipset for the switch! Data that travels over the switch is pretty much pushed through w/o much consideration or impact by the router itself. That's why you can buy an unmanaged Gigabit switch for $20, which certainly doesn't have all that much horsepower and it will work just fine.

So as long as the E3000 has a Gigabit switch, using Gigabit devices and adapters should give you Gigabit speeds. We’re just trying to relieve the router itself from the responsibilities of managing the NAS. And for that, the NAS must be a more powerful, standalone device. If you want to build your own NAS using the old P4 for these purposes, I don’t see a problem w/ it. My only concern might be if the P4 only has PCI and not PCI express (omg, here we go again with complications). PCI is limited to 133MB/s (1000Mbps), which means that in theory, network traffic could consume ALL of the PCI bus. That’s why PCI express was introduced, to add much more capacity to the bus! So while PCI will work, it’s a bit “on the edge” when it comes to supporting Gigabit, esp. if you’re using other PCI devices as well.

That’s why this is more complicated than ppl initially think. There’s a lot of “players” in the Gigabit game that need to be considered, at least if you want the best results possible (did I mention jumbo frames yet? :)  ). But I don’t want to leave the impression that the perfect has to be the enemy of the good. You’d probably be satisfied w/ that P4 as your Gigabit NAS under most circumstances. But it’s good to know its limits so you can make good choices, and perhaps if it comes up short in some circumstances, what might be the problem.
August 27, 2012 12:02:45 AM

Ok, love the response. That having been said, I mostly(I know a fair amount of stuff) understand what you mean with the PCI bus. If you don't mind -- and I know this is asking a lot -- can you shoot me a link on some good reading about pci buses and how they relate to each other? something that will allow me to understand the bus system and its limitations the way you understand them? I think I would be completely totally clear at that point.

eibgrad, you seriously know a lot. its sick. That's amazingly in depth understanding of something that's already in depth.

I assure you that is pure admiration and 0% butt kissing. :D 
September 12, 2012 8:20:17 PM

eibgrad said:
PCI is limited to 133MB/s (1000Mbps), which means that in theory, network traffic could consume ALL of the PCI bus.




I did some reading on this and I've got the general hang of the PCI bus issue you are talking about. The question is, what else runs on the PCI bus on a computer from this era? Seeing as how it has no PCIe, I assume the PCI bus is in heavy use correct?

Does the processor and RAM still have its own bus and will not be affected by this?

I guess what I'm asking is, what's wrong with maxing out the PCI bus with network traffic if the bus isn't needed by other components? (wait, does the USB run on PCI bus?)

thanks for your patience, I'm getting to the nitty gritty of it now:) 

I think I'm just going to plug this hard disk into the USB port on this dimension2400 and use freeNAS on a usb stick. So, if the USB uses PCI bus, then that means I'll have two usb devices AND the nic. AND, one of those USB devices will be the very USB thumb drive that's got freeNAS on it! :o 
September 12, 2012 10:37:15 PM

That's the problem w/ assessing the efficacy of PCI. Sometimes other technologies use it as a backbone. So rather than providing their own bus, they "hitch a ride" on some other bus, particularly a general purpose one like PCI/PCI-E. You often see this when a new technology is introduced that doesn’t have its own bus as yet, so the mobo manufacturer simply uses what’s available. Even when it is available, some mobo manufacturers will still use the PCI/PCI-E bus if only to save money!

So the bottom line, it's very difficult to determine the total extent to which the PCI/PCI-E bus is used by other technologies without examining the motherboard in detail.
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