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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

Skyweir

Level 1

0 points

Jan 6, 2010 4:13 PM in response to Pinthea

Apologies for not getting back promptly on this one. The bottom line from Apple was, if we don't advertise jumbo frames, the purchaser shouldn't expect it. Which should be interpreted as caveat emptor. I thought Apple had quit sacrificing the early adopters, but I got burnt. I could have pursued a return, but the beautiful screen and the hassle (without any assurance of acceptance) of returning it was more than I wanted to do.

My 82 year old neighbor just purchased a 21.5" Core Duo that doesn't support jumbo frames. Do you think she'll ever know? The point I'm making is Apple has played their cards well when one considers how little traffic has been generated by this thread. Additionally, an e-mail I sent to Kasper Jade (Appleinsider.com) regarding this situation was never acknowledged.

Still a shame though, to have hobbled the best iMac (ever) by saving a measly amount. 😟

Pinthea Author

Level 1

20 points

Jan 6, 2010 5:49 PM in response to Skyweir

I was able to confirm that the 27" C2D iMac does support jumbo frames by examining one in the Apple Store. I had also confirmed this on the new 21.5" on the Apple Store floor so I'm somewhat confused by the comment on your elderly neighbor's machine.

As I was able to determine, this issue is a limitation of the ethernet chip used in the quad core motherboards.

My perspective is that the drop of jumbo frames from the quad core machines is not an accident or oversight but a clear decision as a differentiation point between the mainstream/consumer computer (iMac) and their higher end offering (Mac Pro) and I think it's terrible given that we've had jumbo frames for at least a couple of years now.

As a consumer I do not appreciate having a capability taken away that I have become used to, a capability which is still mainstream and not one of those things like serial ports that are removed because they're obsolete, a capability which ENHANCES PERFORMANCE.

Even though the majority of consumers won't give a flip, there are those of us who do and who DO notice. But I guess we're only a blip on the profit radar...

Kind of hard to claim your computers are superior if you're removing "advanced" capabilities for seemingly no reason other than protecting your high end offerings. When marketing decisions rule, you get bad situations like this.

Do I really need to say "Windows machines can do this"? If I did I'd likely be called a Windows fanboy, which I assure you I am not...

Again, I say BOOOOOO.

jleeb

Level 1

0 points

Jan 7, 2010 7:22 AM in response to BrandRealist

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 7, 2010 8:17 AM in response to jleeb

So what you did was lower the MTU size on the ReadyNAS to match that of the i7, so that they were matched at 1500.

Again, not surprising that this situation would give enhanced performance as compared to when one was at 1500 and the other at 9000.

But still not optimal compared to both being set to 9000, which is an impossibility on the i5/i7.

My experience with my former iMac (a 24" C2D 2.66 - early 2009 model) was that when both iMac and NAS were at 9000 the performance was >= 30% or so better than when both were set to 1500.

The performance increase you noticed when setting MTU consistently to 1500 vs. your optimized machine at 9000 could be attributed to your hubs/switches not being jumbo frame enabled.

So when the 9000 packet size left your iMac, the intermediate networking equipment (hub, switch) would have to slice it up, down to a size it could handle (1500) if it was not jumbo frame capable. So then in reality only packets of size 1500 would leave the hub/switch and make it to your NAS, which was expecting 9000 packet sizes.

Worst case, some hubs/switches may actually corrupt or discard mismatched packets. That's not unheard of.

That would certainly lead to the network degredation you indicated, and reducing your MTU to the lowest common denominator (the network switch) would be the most opotimal for your particular setup.

All of my switches are jumbo frame capable, but again, not all are.

Jan 7, 2010 10:01 AM in response to Pinthea

Not all routers and switches don't deal well with jumbo frames (many but not all gigabit ones do, wireless and fast ethernet do not). In fact, a strictly compliant piece of network hardware can't do jumbo frames since the IEEE 802 standards very explicitly set an upper bound of 1500 bytes. If you use jumbo frames, the max goes to 9000, and all devices on the subnet should use the same frame size or the router will have issues (so, if you have a mix of wireless and wired hosts on your network, they should be on different subnets). Mixing jumbo and regular frames will cause big problems, and jumbo frames also introduce latency to the network (shouldn't usually be an issue in a LAN).

jleeb

Level 1

0 points

Jan 11, 2010 7:09 AM in response to Pinthea

Hi,
Thanks for the insight, I had no idea what I was doing so I just made it up, we were amazed when we tested the new settings.

I checked, and all our hardware has j-frame functionality, so I don't know why the performance is so close; could it be the type of data we are sending around the network? In our case it is photo shoots, anywhere from 20-100gb of raw files, jpegs, tiffs, setting files etc, each individual raw file is 20-25mb, and that is mostly what we move around, we wondered if jumbo frames maybe only made a substantial difference with ie video files?

As I said, I'm making this up as I go along, I'm a photographer and I really would rather know as little as possible about something as dull as computer hardware, but thanks to lack of clear support from manufacturers and retailers, we often have to fiddle around under the hood to get things working.

Can you believe that when we bought the NAS box from our Apple approved "Pro" re-seller, I talked them through what I was up to, the exact set-up etc etc, and no-one said - "Hey, have you got a switch?" We were routing through the internet router, but I felt something wasn't right…don't laugh, like I said, I'm mostly self-taught, more through necessity than desire, and it is not amusing to find that the store staff know less about the products than you do, not that that is their fault of course.

Jan 13, 2010 6:10 PM in response to jleeb

jleeb wrote:
Can you believe that when we bought the NAS box from our Apple approved "Pro" re-seller, I talked them through what I was up to, the exact set-up etc etc, and no-one said - "Hey, have you got a switch?" We were routing through the internet router, but I felt something wasn't right…don't laugh, like I said, I'm mostly self-taught, more through necessity than desire, and it is not amusing to find that the store staff know less about the products than you do, not that that is their fault of course.

I won't laugh. I am just glad to see I am not the only one that is mostly self-taught, more through necessity than desire and always seem to know more then the sales person at Apple Specialist resellers.

Jan 27, 2010 11:41 PM in response to Pinthea

I couldn't believe it until i read this thread...

I big BOOOOOO from my side.

This makes me angry about my brandnew iMac27" Core i5

Feb 27, 2010 12:45 PM in response to Pinthea

Pinthea wrote:
My perspective is that the drop of jumbo frames from the quad core machines is not an accident or oversight but a clear decision as a differentiation point between the mainstream/consumer computer (iMac) and their higher end offering (Mac Pro) and I think it's terrible given that we've had jumbo frames for at least a couple of years now.

I don't think it was a marketing decision to "create differentiation". Those are only useful when the customers know about the "differentiation" before the sale, in time to encourage them to purchase the more expensive product. An example of such a marketing limitation would be the limitation in the iBook G4s that restricted them to mirroring mode on external monitors. That limitation was on the technical specification sheet, even if the suspected reason for it wasn't.

Mar 27, 2010 7:59 AM in response to Pinthea

Just discovered this thread after finally having time to look at my slow network and I've got to say, this is massively disappointing.

I've an £1600 i7 that has a relic broadcom ethernet controller that can't handle jumbo frames. Like others here, I store my thousands of RAW photos on a NAS, and MTU limits have massively reduced performance. My 1st generation 20" intel iMac can support jumbo frames for fecks sake!

If Apple made the decision to leave it out in order to differentiate iMacs from Mac Pros, then this is pathetic. If it was the 50p cost saving, then this too... is pathetic. Either way, I'm not happy.

It's a ridiculous decision and I, amongst other 'semi-pro' users with external media are being made to suffer.

What a joke.

Skyweir

Level 1

0 points

Mar 30, 2010 8:18 PM in response to Rob Davies

Sad indeed. Makes you wonder who makes these stupid decisions

jme111

Level 1

0 points

Apr 12, 2010 8:25 PM in response to Pinthea

I have the same problem, tried to set the MTU to 9000 on my new Core i7 iMac, to no avail. I am very disappointed, this day and age, I upgraded from a 24 Intel iMac, and this is turning out to be a downgrade. I have a NAS and am transferring at rates of approximately 10mbs, as opposed to over 50mbs per second that my NAS and switches support.

Apple, please fix this with some update asap, I cannot believe that the NIC is not capable of 9000 MTU, and that this is a simple software/OS/or firmware update.

OSX 10.6.3

sudo ifconfig en0 mtu 9000
ifconfig: ioctl (set mtu): Invalid argument
ifconfig en0 mtu 9000
ifconfig: ioctl (set mtu): Operation not permitted
ifconfig en0
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
media: 1000baseT <full-duplex,flow-control>
status: active

Apr 13, 2010 11:49 AM in response to jme111

The BCM5746 does not support jumbo frames. I got the information from the product description on their website.

Page 4, Table 2.
http://www.broadcom.com/collateral/pg/5764M-PG100-R.pdf

May 14, 2010 2:51 PM in response to Pinthea

This is a hardware issue. Apple chose a cheaper ethernet chipset to increase profits on these devices. If you go to store.apple.com and review the technical specs for various devices, you'll notice that they only mention jumbo frames with Mac Pro devices.

In my case, I just received a new MacBook PRO i7 that cannot support jumbo frames. Imagine my surprise when I purchase a professional-grade device that doesn't work in a commonly configured business network.

*So, as a warning to others I say: If you are planning on purchasing any Apple device other than the Mac Pro, expect it to exhibit subpar performance compared to similarly priced PC offerings.*

aid

Level 1

9 points

May 28, 2010 2:33 PM in response to AppleDeveloper

AppleDeveloper wrote:
In my case, I just received a new MacBook PRO i7 that cannot support jumbo frames. Imagine my surprise when I purchase a professional-grade device that doesn't work in a commonly configured business network.

Same here, albeit with an i5. It is disgusting that a £2000 laptop in 2010 can't support frames greater than 1500 bytes. I love the machine otherwise; but this is just bloody infuriating. I've got networks to debug and this machine just can't do that job 😟

Looking around a little earlier it seems there are some USB Ethernet adaptors that will support Jumbo frames - but that wouldn't do any good for performance.

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