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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

neostar

Level 1

0 points

Jun 4, 2010 11:06 AM in response to aid

Picked up on this story in my Drobo FS review (http://timon-royer.com/en/75/drobo-fs-benchmark-and-review/). Really really disappointing from Apple, performance of the Drobo FS is much better with jumbo frames and I'm screwed with a $2.500 iMac that can't even do jumbo frames.

neostar

Level 1

0 points

Jun 4, 2010 11:36 AM in response to Beeki

@Beeki, I was just reading the PDF (http://www.broadcom.com/collateral/pg/5764M-PG100-R.pdf) The BCM5764 does support jumbo frames! It's only the BCM5784 (page 29) that doesn't. So it's probably something that can be fixed!

Scorpie

Level 1

130 points

Jun 4, 2010 1:20 PM in response to neostar

@neostar, not sure if that's the case -- I'd think that looks more like a typo than saying some other device doesn't support it.

I think everyone else in this thread has focused on the overview table, on page 4 where it says: "Jumbo Frame Support: No".

Of course, we haven't heard from Apple OR Broadcom, so we could only hope. Thanks for the heads up either way.

neostar

Level 1

0 points

Jun 4, 2010 4:14 PM in response to Scorpie

Well might be a typo. Let's see if I get any feedback from the bug report.

Jun 5, 2010 2:36 PM in response to AppleDeveloper

I am in complete shock here. I was thinking of getting a new 17-inch but this stinks. So it seems at though everything that has the i7 and i5 new processors, for some stupid reason, has no support for jumbo frames? It looks as though our previous idea of what was going on was wrong. I am greatly saddened by this news. 😟

neostar

Level 1

0 points

Jun 5, 2010 2:59 PM in response to StephenCCH

Not the Core i5 or i7 is the problem, it's the network chip Apple chose to use that's not supporting jumbo frames. A pro grade notebook and $2k+ iMacs that don't have something that has been standard for years. Those engineers should really get fired for such a stupid decision.

Jun 5, 2010 3:04 PM in response to StephenCCH

I just found out why they do not have Jumbo frame support via http://forums.creativecow.net/thread/8/1084302 in the last post by Steve Modica. This is starting to make more sense now, what Apple is doing.

"I think there's a lot of confusion over the issue of jumbo frames, segmentation offload, and the new i7 performance.

The new imac (and the new Mac Book Pros) use the Broadcom 5764 chipset and it does not support jumbo frames. It supports a feature called TSO (transmit segmentation offload) that is meant to provide jumbo frame performance without the requirement of switch and partner support. Large packets get handed to the card, and it chops them up and applies headers. This saves the OS the trouble. That's all good and true enough.

On the receive side, you still receive 1500 byte packets. The receiver has to strip the headers and reassemble. This takes a lot of CPU. It generates more interrupts and more context switches. It causes more work for the server. One solution to this is receive side coalescing, but no gigabit chips today support that. (The Intel 82599 10Gb chip on our newest 10Gb card does). So for the present, when an imac is reading in video, there's 0 jumbo frame "help" so to speak. It's full on tiny packets."

Jun 5, 2010 3:08 PM in response to neostar

neostar wrote:
Not the Core i5 or i7 is the problem, it's the network chip Apple chose to use that's not supporting jumbo frames. A pro grade notebook and $2k+ iMacs that don't have something that has been standard for years. Those engineers should really get fired for such a stupid decision.

Of course the processor has nothing to do with the networks chip. I was meaning only Macs with the new processors have these new network chips that do not support Jumbo Frames. Therefore all i7 and i5 Macs have this disability.

neostar

Level 1

0 points

Jun 5, 2010 3:18 PM in response to StephenCCH

@StephenCCH, then we're on the same page. Thanks for the additional info, that clears it up quite a bit. I still don't get why Apple made such a decision for the high end product line.

Jun 5, 2010 3:35 PM in response to neostar

@neostar,
Yes, we certainly are. I think what is really going to tell all, is when the MacPro is updated.

Message was edited by: StephenCCH

neostar

Level 1

0 points

Jun 16, 2010 4:00 AM in response to StephenCCH

Ok, got the final answer from Apple on my bug report. This chipset is unable to support jumbo frames! No chance whatsoever, you're officially screwed if you rely on jumbo frames and an iMac.

Apple is making a lot of bad decisions lately, censoring apps that are completely legal in the country they would sell, very closed model for their bookstore which upsets publishers, killing long time available pro features in advertised pro products like the iMac, a new Mac mini priced at a point where it's hard to justify buying it.

Apple isn't the company it used to be and that is a bad thing.

Jun 16, 2010 6:11 AM in response to neostar

Nice. Thanks Steve.. I have spent 3000$+ on gear that will not work as good as needed...

Anyway I think they quietly realized this mistake. Take a look at new Mac Mini specs:

http://support.apple.com/kb/SP585

"10/100/1000BASE-T Ethernet (RJ-45) interface with support for *jumbo frames*"

Same spec KB site for MacBook Pro 17" (mid 2010) got that part missing...

Can Genius Bar re-solder new Broadcom chip for me? 🙂

neostar

Level 1

0 points

Jun 16, 2010 6:19 AM in response to eddiechapman

The real problem with this is, Apple screwed their customers for years. You can only use jumbo frames on a network if all devices including the switch support it. So when you have a single device in your network like the latest iMacs that don't support it degrades the whole network for years to come.

I've tested it myself and the performance drops dramatically when you enable jumbo frames on the Drobo FS and your system doesn't support it, way below what you get with an MTU size of 1500.

Jun 16, 2010 2:12 PM in response to eddiechapman

@eddiechapman
If you are referring to me, you are welcome. If you are referring to Steve Jobs, well never mind.

They didn't use an i3, i5 or i7 with the new Mac mini therefore I was expecting it to support Jumbo Frames!

Don't forget that the mini comes with a Core2Duo therefore it should support it, according to the theory (and history so far) we have been working on. Now if Apple ever comes out with a i5 or i7 Mac that supports Jumbo Frames then they will be changing course.

InsjaHH

Level 1

0 points

Jun 28, 2010 12:52 AM in response to aid

I've recently purchased my (first) Macbook Pro 13" Early 2010 (2.4GHz, 4GB, Intel X25-MG2 160GB) and I was really disappointed to see that there is no support for jumbo frames at all.

Although it's a C2D, it has a Broadcom 5764 chip which apparently does not support jumbo frames at all. I'm guessing this is it then, no driver support for Snow Leopard can turn this feature on, am I correct?

I still have to do some iPerf testing, just to see what performance I'm actually getting with everything else on jumbo frames support (and the Macbook Pro not).

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