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Pinthea Author

Level 1

20 points

No jumbo frames (MTU 9000) with new Core i5 iMac?

Discovered today that my day-old iMac Core i5 is missing the option to set MTU to 9000 (to enable jumbo frames). When in my network settings I have only options "Standard (1500)" and "Custom" and when I choose "Custom" the entry field shows allowed values of 72 - 1500. If I try setting to 9000 then it gets set to 1500. I used to have a "Jumbo (9000)" option with my previous 24" iMac (C2D) which I sold a couple of weeks ago. So I know my network hardware supports it, and having it set to Jumbo is very helpful in getting increased network throughput to my NAS.

To confirm, yes -- I am trying to set this via Ethernet settings and not AirPort. This issue occurs in "Automatic" network location and in any new ones I set up (such as "Home"). Also applies to any new users I try to create as a troubleshooting aid. I have bounced the gigabit ethernet switch I am connected to, just in case... I have not yet tried reinstalling 10.6.2 from the disc that came with the machine since I just brought it home from the Apple Store today!

The other network options on the "Ethernet" tab are:

Configure: Manually
Speed: 1000baseT
Duplex: full-duplex, flow-control
MTU: Standard (1500) or Custom (my only 2 choices)

Can anyone confirm that MTU 9000 (Jumbo Frames) is or is not enable-able on your Core i5 or i7 iMac?

THANKS!

Message was edited by: Pinthea

Message was edited by: Pinthea

iMac 27" Core i5, Mac OS X (10.6.2)

Posted on Nov 16, 2009 6:40 PM

90 replies

Beeki

Level 1

0 points

Nov 26, 2009 12:48 PM in response to Rotortalk

I guess so as I think that i7 and i5 machines use the same mobo.

Check System Profiler -> Ethernet Cards

Vendor ID: 0x14e4 (Broadcom)
Device ID: 0x1684 +(BCM5764 NetXtreme Desktop/Mobile)+

Why must be combination of cost and power-consumption, and propably 95% of users wont care.

Pinthea Author

Level 1

20 points

Nov 26, 2009 1:02 PM in response to Beeki

Wow, Apple, that's really pathetic. What, you save 10 cents a chip by going with a lesser capable ethernet chip than any you've released in any other iMac in the last 2 years?

Oh, I get it. You're trying to reduce the potential perception that the quad core iMac is just as good/capable for higher-end things as a Mac Pro by limiting the iMac's 'advanced features'?

When the 21.5" has more capable ethernet capabilities than the 27, that's wrong.

And this feature DOES matter to your consumers who are paying TOP DOLLAR for your product, even if it's only 5% of them.

You took something away that we have come to depend on...

Either way, all I can say is BOOOOOOO.

Maybe you should have put a 56K modem in it, too. Or maybe just an 802.11b capable WiFi adapter. I hear those are cheap these days, too... "Proudly engineered in California." Yeah.

Karen

Level 2

269 points

Nov 26, 2009 1:18 PM in response to Pinthea

I've got a Mac Pro that supports Jumbo Frames. My network routers are set for Jumbo Frames. But, all the same, the Network panel under Snow Leopard refuses to allow me to set it for MTU 9000. So I don't think that this is just an iMac problem.

However, using the terminal command "sudo ifconfig en0 mtu 9000" (and for en1 as well) does actually set the MTU to 9000. So it may well be that the iMac does not support it in hardware (which would be disappointing).

Pinthea Author

Level 1

20 points

Nov 26, 2009 2:25 PM in response to Karen

Unfortunately it's not a user interface issue which prevents setting jumbo frames on the new quad core iMacs...

Having previously verified that "sudo ifconfig..." will NOT work on the i5 to set MTU > 1500, and that is no doubt due to the fact (which I just verified from Broadcom's own technical documentation) that the Broadcom chip in the i5 iMac is simply not capable of jumbo frames.

And there's no possibilty of that ever changing with any sort of update from Apple since it's a limitation of the actual chip in use and not of driver support or of firmware.

But it's not this way on any of the 21.5" C2D iMacs I checked, nor is it that way on the 27" C2D iMac, only on the (27") quad core iMacs. As though that 'advanced functionality' was intentionally crippled on the new iMac quad cores by Apple's choice of ethernet chip. Booooooooo.

Karen

Level 2

269 points

Nov 27, 2009 2:54 AM in response to Pinthea

I agree totally - it is a strange decision to fit a more limited ethernet chip to the i5/i7 iMacs as compared to the C2D Macs.

And it is a pain that Snow Leopard doesn't seem to let you set the MTU properly either and that you need to revert to the terminal (so thanks very much for the terminal commands).

Skyweir

Level 1

0 points

Dec 9, 2009 11:05 AM in response to Pinthea

I too contacted support. I was immediately bumped to the next tier then told this would be discussed with an engineer. I'll hear back in 3 to 5 days. I was assured if Apple couldn't solve this problem to my satisfaction, a refund would be issued.

Pinthea Author

Level 1

20 points

Dec 9, 2009 12:36 PM in response to Skyweir

PLEASE follow up with us on this thread to let us know how things turn out...

Not sure what they can do exactly, given that it's a limitation of the hardware (gigabit ethernet chip in use).

I really notice the slower network throughput to my NAS with the limit of MTU = 1500...

Thanks!!!!!!

Skyweir

Level 1

0 points

Dec 9, 2009 5:54 PM in response to Pinthea

If Apple has willingly done this, it seems rather stupid.

What ethernet controller is currently used in the Core Duo? Is it pin compatible with the 5764? Call me madcap, but is it possible there was an error in the quad core motherboard assembly whereby the wrong chips were utilized?

Dec 12, 2009 7:04 PM in response to Pinthea

I discovered this issue as well with my new iMac 27" i7, thought how annoying this is considering with my Macbook Pro I relied on the jumbo frames to get me a nice performance improvement from my ReadyNas NV+.

However this morning I did a speed test and without Jumbo frames the iMac is getting similar speeds to the Macbook Pro with jumbo frames. This is so far been the best apple computer I've had out of the two, the Macbook Pro on the other hand is a whole different story, bloody disaster, its in for repairs again for problems Ive had to put up with since I bought it almost 3 years ago.

Dec 18, 2009 2:05 AM in response to Karen

It sounds like they might be moving away from Jumbo frames, since Snow Leopard won't let you set it on a Mac Pro. Very disappointing.

Skyweir

Level 1

0 points

Dec 19, 2009 2:08 PM in response to BrandRealist

BrandRealist , Think about how much faster your transfers might be if Apple had used a controller capable of supporting jumbo frames. I would agree, this is the best Mac I've ever owned, but this is a deal breaker for those of us pushing terabytes of data over our networks (i.e. video editing). I expected improved performance from a top of the line iMac.

SteveCCH, I don't think Apple is moving away from jumbo frames. Your problem could be related to a GUI issue in network prefs. Have you tried enabling jumbo frames and then checking the results in Apple System Profiler?

Dec 28, 2009 11:04 PM in response to Pinthea

Skyweir, Unfortunately I have to agree with you now, since my last post I have since discovered that while their is a small reduction in read spead off my ReadyNas NV+, there is a significant reduction on the write speed without jumbo frames. This is frustrating as I do regularly move gigabytes of data around the network. One of the reasons why I bought the iMac was so I can do photo processing of my Raw images with a main desktop machine that is much faster than the old Macbook Pro, however it looks like I will need to use the macbook pro at the very least to move large quantity of files around if needs be. Very frustrating when you consider that its unheard of a network controller not having jumbo frames these days. Even my partners PC which has an integrated ethernet controller on the main-board supports jumbo frames.

I have to admit its very poor on apple, and the only option I see around this problem which would allow me to keep the iMac would be to upgrade the ReadyNas NV+ to a NVX which apparently has some decent write and read speeds without jumbo frames.

Seriously what was Apple/Steve thinking when they made this extremely fast 27" screen iMac and then to bottle neck it with a sub-par ethernet controller.

Perhaps Apple will buy my old ReadyNas Unit off me for $1000 (including 4x500gig disks) just so I can upgrade ? I think not.

I knew I should have built my own PC and just gone back to windows, I hear windows 7 isn't too bad. But the screen on the iMac is lovely, oh decisions decisions.

Jan 5, 2010 12:28 PM in response to Skyweir

Skyweir, I was replying to Karen. Sorry, I didn't make that more clear. I wish I did have a Mac Pro though 🙂.

Now that I am running Snow Leopard on the MBP, I can say from experience that Jumbo Frames work just fine in 10.6. Therefore, it looks as though Apple is not moving away from Jumbo Frames after all.

jleeb

Level 1

0 points

Jan 6, 2010 11:15 AM in response to Pinthea

Hi,
We have just discovered a counter-intuitive tweak which has somewhat cut read times and dramatically cut write times between an i7 and a Readynas NV+.

Simply go to your Readynas set up page/Network/Interface and untick 'Enable jumbo frames'. I also changed the MTU setting to 1500 just to be sure.

Write time (mac to server) for a 10gb file went from 30-ish mins to 9-ish mins, and read time (server to mac) 7-ish mins to 4mins 15secs.

We previously had an iMac 3.06ghz with all optimal settings on the mac and the server, jumbo frames etc etc and so the network performance of the new machine was very disappointing, but this seems to have recovered most of our performance.

I know this seems weird, thought I'd share, hopefully it's not too good to be true...

Anyway hope this helps!

J

Pinthea Author

Level 1

20 points

Jan 6, 2010 11:26 AM in response to jleeb

First and foremost, as you described, it is important for the NAS and your iMac to agree on what the MTU is going to be. If they're set differently, then packet fragmentation will occur and that introduces inefficiencies and what-not, and the impact is reduced throughput.

WHEN the NAS and iMac agree on MTU, be it 1500 or 9000, that is the best situation and the packet sizes will align.

BUT, when both are set to 1500, you will get different performance than when they are both set to 9000.

My experience is that when both set to 9000, performance is superior.

Unfortunately Apple's awkward choice of ethernet chip in the Core i5 iMacs absolutely and completely removes the ability to specify MTU of 9000 on the iMac, therefore removes the ability for you to get increased performance over the 1500 setting.

No jumbo frames (MTU 9000) with new Core i5 iMac?