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post #1 of 18 Old 01-20-2009, 04:45 PM - Thread Starter
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if everything in my setup supports jumbo frames - is there any reason not to use it?

my server/htpc nics support it. I have linksys SD2008 v3 which also supports jumbo frames.

if so - what are the differences between all the 2-9kb MTU's?

Thanks

Ryan
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post #2 of 18 Old 01-21-2009, 11:13 AM
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The way it's been explained to me and I've seen results to back it up are that the higher the MTU the faster the transfer can be with larger blocks (large singular files). When you have lots of smaller files (images, mp3s, documents) the benefit decreases rapidly as you spend more time caching files than transferring them. If you have any signal quality issues at all, do not mess with Jumbo Frames as that would just make things worse with resent packets.

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post #3 of 18 Old 01-21-2009, 11:54 AM
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I found I needed to use Jumbo frames (9K) in order to get any decent speed out of my Gigabit NIC's.
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post #4 of 18 Old 01-21-2009, 01:29 PM
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I love the speed when transferring 8GB+ files between my PCs, jumbo frames makes a big difference in throughput!
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post #5 of 18 Old 01-21-2009, 01:57 PM
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Quote:
Originally Posted by jhhoffma View Post

The way it's been explained to me and I've seen results to back it up are that the higher the MTU the faster the transfer can be with larger blocks (large singular files). When you have lots of smaller files (images, mp3s, documents) the benefit decreases rapidly as you spend more time caching files than transferring them. If you have any signal quality issues at all, do not mess with Jumbo Frames as that would just make things worse with resent packets.

jhhoffma,

Do you know of any software (freeware?) that can analyse a LAN channel link for any issues. I know there a qualification/certification testers but a software one would be much easier/cheaper than buying/renting one of those testers for a couple of links tests?
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post #6 of 18 Old 01-21-2009, 03:20 PM
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Iperf? It'll test the capacity of the line, but I'm not aware of any full-blown network analysis tool. That stuff would make serious money in the IT world, so it's unlikely to be found for free (unless the Linux geeks figured one out).

I have 4k packets on my network as that's the highest number that all my NICs are capable of. Plenty of speed (30-50MB/s) on my network even when it's slow.

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post #7 of 18 Old 01-21-2009, 04:20 PM
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I'll try and work out Iperf. Thanks

The highest I have ever seen on my "gigabit" network segment with 7k frames transferring 0.99GB vob files is 18MB/s. Average is around 9-12 MB/s I've always thought my network was slow.

I've attached a diagram of my setup. It uses Cat5e.

Any ideas?
LL
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post #8 of 18 Old 01-21-2009, 05:00 PM
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Jumbo frames will usually increase performance to an extent. It greatly reduces the load on the CPU as well because instead of sending 1500KB packets, you're sending 2 to 6 times that per packet, reducing overall packet transmission.

Every setup is different, I'd suggest staring at the 4K range and working up and see which MTU setting works best for you. I found once I got to 6K, there was no material difference by increasing the MTU further.
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post #9 of 18 Old 01-21-2009, 09:23 PM
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Remember that you're also limited by the write speed of the drive and subsystem your copying to. So if it's an older system, you may not be able to wring any more out of it.

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post #10 of 18 Old 01-21-2009, 10:23 PM
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Quote:
Originally Posted by wooddog View Post

jhhoffma,

Do you know of any software (freeware?) that can analyse a LAN channel link for any issues. I know there a qualification/certification testers but a software one would be much easier/cheaper than buying/renting one of those testers for a couple of links tests?


To simply test what max packet size the machines on your network can handle, open a command prompt;

ping -f -l

If you don't see 'packet needs to be fragmented....' it's good.
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post #11 of 18 Old 01-21-2009, 11:25 PM
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Well I've succeeded in hijacking the OP's thread. Sorry, maybe you can get something out of this too.

1472 bytes is the max ping before "packet needs to be fragemented but DF set" occurs

The laptop is an asus f3sc, max frame size set to 4000

DNS-323 is set to jumbo frame 4K MTU. Both GbE NICs through Netgear GS605 switch as per my picture posted earlier.

In this case, both patch cables are Krone ADC Cat5e. When using my HTPC the permanent link is about 25m.

Any ideas? Surely I can get better speeds.
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post #12 of 18 Old 01-21-2009, 11:37 PM
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Most commercial drives have a sustained write limit of around 70-100MB/s. Read limits not too terribly much higher.

100MB*8 = 800mbps at the drive's fastest speed, more likely you'll end up in the 50-80MB/s range which is only around 400-640mbps. We consistently achieve 400-600mbps w/o jumbo frames.

You find support for jumbo frames being necessary for things like storage appliances and high volume storage arrays as they are multi-drive and hardware raided and can reach access speeds past 100MB/s / 1000mbps.
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post #13 of 18 Old 01-22-2009, 06:54 AM
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Quote:
Originally Posted by wooddog View Post

Well I've succeeded in hijacking the OP's thread. Sorry, maybe you can get something out of this too.

1472 bytes is the max ping before "packet needs to be fragemented but DF set" occurs

The laptop is an asus f3sc, max frame size set to 4000

DNS-323 is set to jumbo frame 4K MTU. Both GbE NICs through Netgear GS605 switch as per my picture posted earlier.

In this case, both patch cables are Krone ADC Cat5e. When using my HTPC the permanent link is about 25m.

Any ideas? Surely I can get better speeds.

If both your client network adapters are properly configured for 4k frames, then I would start by looking at the Netgear switch.

I believe Netgear had problems with some versions not properly supporting jumbo frames. You'll need to dig a little to see if your version or serial nbr falls into that batch. The V1 series doesn't support it according to Netgear's site
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post #14 of 18 Old 01-22-2009, 07:01 AM
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In "most" home scenarios, Jumbo Frames will provide little to no benefit. Jumbo Frames is all about reducing CPU usage, not increasing network throughput. 1gbps is 1gbps. You should be able to max it out assuming your network is setup correctly, and is functioning optimally, regardless of the packet size. Your CPU usage may be higher with the standard TCP packet of 1400 bytes, but so what? If you can't max it with standard packets, 99.99% you won't be able to max it out with Jumbo frames either.

Look into your source HDDs, target HDDs, NIC cards, switch, router etc before playing with jumbo frames. Those are way more critical than jumbo frames.
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post #15 of 18 Old 01-22-2009, 09:09 AM
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When i stream high def to my htpc over a wireless n network, it gets choppy every 10mins. It plays fine for 10mins then gets choppy for 1min,, then the cycle repeats. I'm using the DIR-655 and D-link wireless N usb adapter. I know bandwidth is not a issue because i can transfer the movie file in 10 mins. Does my problem have anything to do with jumbo frames? Thanks.
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post #16 of 18 Old 01-22-2009, 09:57 AM
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I don't need jumbo frames to hit >70 MB/sec network speeds with properly configured operating systems and decent network interfaces. I've seen up to 110 MB/sec in cached CIFS transfers between e1000e controllers running NT6 and Linux.
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post #17 of 18 Old 01-22-2009, 10:34 AM
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Quote:
Originally Posted by tester3001 View Post

When i stream high def to my htpc over a wireless n network, it gets choppy every 10mins. It plays fine for 10mins then gets choppy for 1min,, then the cycle repeats. I'm using the DIR-655 and D-link wireless N usb adapter. I know bandwidth is not a issue because i can transfer the movie file in 10 mins. Does my problem have anything to do with jumbo frames? Thanks.

No, it has to do with the fact that your streaming HD material over wireless and getting packet loss/resend causing stutters every so often.

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post #18 of 18 Old 01-23-2009, 01:20 AM
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Quote:
Originally Posted by MiBz View Post

If both your client network adapters are properly configured for 4k frames, then I would start by looking at the Netgear switch.

I believe Netgear had problems with some versions not properly supporting jumbo frames. You'll need to dig a little to see if your version or serial nbr falls into that batch. The V1 series doesn't support it according to Netgear's site

My switch is a V2 model supporting jumbo frames.
I have been doing a bit of the ol' googling and discovered that the atheros L1 adapters in my F3SC are considered really low end anyway. I'll disable jumbo frames on all of my devices and do some testing to see what the bottleneck is.
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