Mac Pro v iMac i5/i7 - another iMac limitation

Discussion in 'Mac Pro' started by PaulD-UK, Feb 26, 2010.

  1. PaulD-UK macrumors member

    Joined:
    Oct 23, 2009
    #1
    Hi
    Seems the ethernet chip in the 27" i5/i7 iMacs isn't capable of handling jumbo frames - the 27"/21" core 2 duo iMac and other older ones had no problem with 9000 jumbo ethernet packets.

    Which hobbles the bandwidth connectivity for central storage SAN users - video and the like:
    http://forums.creativecow.net/thread/8/1076136
     
  2. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
    Location:
    Singapore
    #2
    wow how very interesting!!

    is this a simple firmware fix? or a hardware limitation?

    for those of us that are less knowledgeable, can you explain it a bit more? jumbo packets refers to the size of the packets no? 9000bytes instead of the normal 1500bytes?
     
  3. PaulD-UK thread starter macrumors member

    Joined:
    Oct 23, 2009
    #3
    Hi
    Here's what the guy writes in his blog - follow link in the Cow thread:
    ...the Broadcom 5764 Ethernet Controller in the i7 iMac 27″ does not support speeds over 1500. This same controller is in the i5 iMac 27″ machine too. ...the Broadcom website is very vague as to whether the controller itself cannot support higher speeds or if it’s just a driver issue. I’ve been told by outside sources that the documentation on the 5764 states it does not support Jumbo Frames...

    There is software for any Mac that supports jumbo frames to optimise transfer speeds and minimise latency to allow video editing using a compressed HD or SD format - usually ProRes 422 - from a SAN.
    You use wi-fi for other ethernet connectivity.

    ...achieved robust performance and nearly $25,000 in cost savings with the installation of a 16TB shared storage system featuring Small Tree’s GraniteSTOR products and unique OS X networking technology, which supports multiple Ethernet ports tightly integrated with Apple’s built in file sharing application. By installing the GraniteSTOR solution, consisting of Small Tree’s PEG4, a 4-port Ethernet card and Edge-corE ES4524D, a 24-port Gigabit Ethernet switch certified to work with Small Tree’s technology, BCM is running six real-time streams of compressed HD across Gigabit Ethernet.
    http://www.small-tree.com/Articles.asp?Id=336

    ie The SAN storage is hung off a Mac Pro which connects via a 4-port gigabit PCI-e card using Link Aggregation to a managed gigabit switch, which then runs over a single ethernet cable to the edit-station Mac.

    With a proper gigabit port using jumbo frames the Mac will get up to about 100MB/s connectivity to the 16TB storage.
    Only with the new i5/i7 iMacs you don't :(
     
  4. Dzokayi macrumors member

    Joined:
    Mar 12, 2009
    #4
    interesting find...

    ...thanks for posting. Going to keep an eye on this; some folks could be unpleasantly surprised.
     
  5. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
    Location:
    Singapore
    #5
    im somewhat confused. 1500mb/s? of course it wont support speeds faster then that :-S
     
  6. thedarkhorse macrumors 6502a

    Joined:
    Sep 13, 2007
    Location:
    Canada
  7. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
    Location:
    Singapore
    #7
    yes. i am WELL aware of that.

    i simply inquired how can the iMac recieve 1500MEGABITS PER SECOND when its clearly meant for 1000MEGABITS PER SECOND.

    clear enough? :rolleyes:

    ignore the formatting of the thing and just look at the capitalisation is all im saying.... if i meant MB/s i would have used capaitals.
     

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