What is true GigaBit speeds? I thought I had it

Posted:
in General Discussion edited January 2014
I have a netgear gigabit router

I bought a WD World Book NAS that's also gigabit.



I have cat6 running to each device



Intel Mac Pro Tower > Cat 6 Cable >> Gigabit Router << Cat 6 Cable < WD World Book



I'm coping a huge load i'm at 105.5 GB of 820GB, says 25 hrs, but the speed seems about 35% capacity of gigabit.. i'm copying from my mac pro to my WD NAS..



I have no other apps running.. should it really be taking that long.



I did a google search, they're saying that Cat6 is 600Mbps not true 1,000???



Do I need Cat7 Cable to get true Gigabit transfer speeds?
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  • Reply 1 of 26
    hirohiro Posts: 2,663member
    Quote:
    Originally Posted by domerdel2 View Post


    I have a netgear gigabit router

    I bought a WD World Book NAS that's also gigabit.



    I have cat6 running to each device



    Intel Mac Pro Tower > Cat 6 Cable >> Gigabit Router << Cat 6 Cable < WD World Book



    I'm coping a huge load i'm at 105.5 GB of 820GB, says 25 hrs, but the speed seems about 35% capacity of gigabit.. i'm copying from my mac pro to my WD NAS..



    I have no other apps running.. should it really be taking that long.



    I did a google search, they're saying that Cat6 is 600Mbps not true 1,000???



    Do I need Cat7 Cable to get true Gigabit transfer speeds?



    For reality you aren't doing too bad. Better cables may help a bit, but there are a couple issues that reduce user measured throughput compared to max theoretical throughput.



    One is numeric base transitions 1Gbit is one billion bits (1 x 10^9), but when you transfer files and the OS displays the results the file size is measured in binary so the binary equivalent is (2^30). 2^30 == 1,073,741,824 which is bigger than 1,000,000,000, so even when everything is running at max theoretical you could only measure an apparent ~93% throughput.



    Second, you could only get max throughput if there are no collisions, collisions can bring a network entirely to all stop if you try to push somewhere in the neighborhood of 70% capacity through it, because every collision doubles the amount of bandwidth that packet takes.



    Third, unless you are doing something like using unreliable UDP, the receiving machine sends back an acknowledgment, a packet totally unmeasured by a naive throughput metric. Those ACKs also raise the collision probability significantly. Double trouble for the throughput measurement.



    There are other router related network issues, things that are overall very good for connecting to the world, but may help sub-optimize (just a little) a local machine to machine transfer, especially if you have multiple machines connected to the router. All that backbone overhead doesn't consume much bandwidth itself, but it does impact collision probability when you try to max out a local file transfer.



    So a true 350Mbit isn't horrible. I'm sure there are some sysadmins around who can provide specifics on how to improve that some but you won't ever see anything near true Gbit transfer speeds using TCP traffic on a 1Gbit system.
  • Reply 2 of 26
    Quote:
    Originally Posted by Hiro View Post


    For reality you aren't doing too bad. Better cables may help a bit, but there are a couple issues that reduce user measured throughput compared to max theoretical throughput.



    One is numeric base transitions 1Gbit is one billion bits (1 x 10^9), but when you transfer files and the OS displays the results the file size is measured in binary so the binary equivalent is (2^30). 2^30 == 1,073,741,824 which is bigger than 1,000,000,000, so even when everything is running at max theoretical you could only measure an apparent ~93% throughput.



    Second, you could only get max throughput if there are no collisions, collisions can bring a network entirely to all stop if you try to push somewhere in the neighborhood of 70% capacity through it, because every collision doubles the amount of bandwidth that packet takes.



    Third, unless you are doing something like using unreliable UDP, the receiving machine sends back an acknowledgment, a packet totally unmeasured by a naive throughput metric. Those ACKs also raise the collision probability significantly. Double trouble for the throughput measurement.



    There are other router related network issues, things that are overall very good for connecting to the world, but may help sub-optimize (just a little) a local machine to machine transfer, especially if you have multiple machines connected to the router. All that backbone overhead doesn't consume much bandwidth itself, but it does impact collision probability when you try to max out a local file transfer.



    So a true 350Mbit isn't horrible. I'm sure there are some sysadmins around who can provide specifics on how to improve that some but you won't ever see anything near true Gbit transfer speeds using TCP traffic on a 1Gbit system.





    WoW! first off thank you for the elaborate response. Here's the Get info off the mapped Volume Drive:

    afp://MyBookWorld._afpovertcp._tcp.local/Public



    so it's some translation of AFP to TCP ? How much is lost there?



    I'm also wondering if i just plugged it in directly to the secondary ethernet port on my mac pro.. for NAS it could be a straight patch or cross-over? i'm not saying I'll do that, but in the future, would it:



    1. less of collision for higher speeds

    2. need crossover?



    I'd try it right now, but i'm making a massive transfer as we speak.
  • Reply 3 of 26
    Unfortunately, Hiro's response is, um, mostly wrong.



    First, you don't have any collisions (well, unless there's something wrong with the Mac or the Router). I'm not going into long detail, but feel free to lookup collision domains. Collisions are _pretty much_ only an issue on shared networks (read: hub, not switch).



    Your issue is mostly hard drive read and write limitations. A fair average sustained read throughput would be in the 60-75 MB/s, and average write throughput is in a similar range. This assumes both drives are modern 7200 RPM drives. Both read and write speeds have increased a lot in the past couple of years, so even a "top of the line" drive that's 2 years old might be outperformed by a middle of the road drive released today.



    Then, you need to consider the overhead associated with packetization of data into TCP...the theoretical max data throughput (sometimes called "goodput") is .94% of the link speed. A much more realistic average is about .75% of link speed.



    So, you're looking at something like 60MB/s * .75 = 45MB/s = 360Mbps



    If either drive is a bit slow, that 360Mbps starts dropping pretty quickly. There's also a lot of variability in read and write speeds from the beginning to the end of a drive.



    Hiro is right in mentioning GB vs GiB...If the OS reports 105.5GB that's actually about 113,279,762,432 Bytes. Multiply that by 8 to get 906,238,099,456 bits.



    906,238,099,456 bits / 360,000,000bps = about 42 minutes in a perfect world



    I'd be really curious to hear how long your transfer actually took.







    Quote:
    Originally Posted by domerdel2 View Post


    WoW! first off thank you for the elaborate response. Here's the Get info off the mapped Volume Drive:

    afp://MyBookWorld._afpovertcp._tcp.local/Public



    so it's some translation of AFP to TCP ? How much is lost there?



    I'm also wondering if i just plugged it in directly to the secondary ethernet port on my mac pro.. for NAS it could be a straight patch or cross-over? i'm not saying I'll do that, but in the future, would it:



    1. less of collision for higher speeds

    2. need crossover?



    I'd try it right now, but i'm making a massive transfer as we speak.



  • Reply 4 of 26
    MarvinMarvin Posts: 14,195moderator
    Quote:
    Originally Posted by domerdel2 View Post


    Do I need Cat7 Cable to get true Gigabit transfer speeds?



    Faster hard drives. If your drives read/write at around 80MB/s, which is near the upper end of a 7200 rpm drive, your transfer rate can only ever be 80 x 8 = 640Mbps.



    If you get a RAID system, you might push it higher but there are some network overheads already mentioned.
  • Reply 5 of 26
    Quote:
    Originally Posted by concentricity View Post


    Unfortunately, Hiro's response is, um, mostly wrong.



    First, you don't have any collisions (well, unless there's something wrong with the Mac or the Router). I'm not going into long detail, but feel free to lookup collision domains. Collisions are _pretty much_ only an issue on shared networks (read: hub, not switch).



    Your issue is mostly hard drive read and write limitations. A fair average sustained read throughput would be in the 60-75 MB/s, and average write throughput is in a similar range. This assumes both drives are modern 7200 RPM drives. Both read and write speeds have increased a lot in the past couple of years, so even a "top of the line" drive that's 2 years old might be outperformed by a middle of the road drive released today.



    Then, you need to consider the overhead associated with packetization of data into TCP...the theoretical max data throughput (sometimes called "goodput") is .94% of the link speed. A much more realistic average is about .75% of link speed.



    So, you're looking at something like 60MB/s * .75 = 45MB/s = 360Mbps



    If either drive is a bit slow, that 360Mbps starts dropping pretty quickly. There's also a lot of variability in read and write speeds from the beginning to the end of a drive.



    Hiro is right in mentioning GB vs GiB...If the OS reports 105.5GB that's actually about 113,279,762,432 Bytes. Multiply that by 8 to get 906,238,099,456 bits.



    906,238,099,456 bits / 360,000,000bps = about 42 minutes in a perfect world



    I'd be really curious to hear how long your transfer actually took.



    Thank you all for the input. Keep subscribed to this post and i'll let you know the amount and duration it took to transfer as is.
  • Reply 6 of 26
    Quote:
    Originally Posted by Marvin View Post


    Faster hard drives. If your drives read/write at around 80MB/s, which is near the upper end of a 7200 rpm drive, your transfer rate can only ever be 80 x 8 = 640Mbps.



    If you get a RAID system, you might push it higher but there are some