Hard Drive bandwidth

Discussion in 'MacBook' started by softwareguy256, Apr 14, 2012.

  1. softwareguy256 macrumors regular

    Joined:
    Jun 5, 2010
    #1
    I tried getting some crude benchmarks to see if I should upgrade to a SSD. I basically went to an applestore opened up a command prompt and typed:
    grep -r a *
    grep -r a * > largefile.txt

    and measured the disk activity in activity monitor.
    Macbook Air: 250 MB/Sec peak
    Macbook pro 17'': 100 MB/sec peak
    My 2009 macbook: 18 MB/sec peak <-- wtf?

    With an external 10k western digital raptor drive hooked up to usb 2.0 I am getting about 40 MB/sec peak.

    At this point I cannot rule out that the macbook logic board is not a bottleneck, which is preventing me from buying a $400 SSD drive upgrade. I read the return policy on Newegg, there is none, only exchange. I would only upgrade if I could get performance similar to macbook air I saw today.

    What peak disk access do others with macbooks get?
     
  2. simsaladimbamba

    Joined:
    Nov 28, 2010
    Location:
    located
    #2
    I got at least 75 MB/s with my 2008 MacBook and a 160 GB HDD (5.400 RPM). Maybe your HDD is failing?
     
  3. Intell macrumors P6

    Intell

    Joined:
    Jan 24, 2010
    Location:
    Inside
    #3
    Try doing "cd /" then "grep -r a * > largefile.txt". If there isn't much stuff for it to list, it won't reach its peak speed.
     
  4. davidg4781 macrumors 68010

    Joined:
    Oct 28, 2006
    Location:
    Alice, TX
    #4
    Hrm. I got 122 on my 2006 CD MacBook. It has a 7200 HDD. If I'm looking at the right place.
     
  5. throAU, Apr 24, 2012
    Last edited: Apr 24, 2012

    throAU macrumors 601

    throAU

    Joined:
    Feb 13, 2012
    Location:
    Perth, Western Australia
    #5
    Your crude benchmark will not take disk fragmentation or file size into account (likely explains why your own macbook is so slow) - many large files = faster than many small files.

    However, in terms of IOs per second (which generally is a more useful measure than megabytes per second) under random IO, for reference:

    7200 rpm data = ~70-80 per second (this is as fast as the heads can re-position for random reads)
    SSD = 4000-8000+ per second (no head repositioning time).


    If you're streaming large, non-fragmented files a hard drive will perhaps get 100-120 meg per second (vs say 200-300 for an SSD). If you're doing random 4k reads, that may drop to 300k per second (75-80 IO operations x 4k per sec).

    An SSD will stay fast (up around 200 meg per second) doing random IO.


    THAT is why an SSD kills for performance in most day to day things - multi-tasking disk access is not totally random, but its not very sequential. Even if your SSD only did 80 meg per second, it will still be faster than a spinning disk for most day to day use, because most day to day use (other than file copies) doesn't involve sequential streaming. Even a "slow" SSD will be far more responsive.


    Even if your IO controller on your macbook is a bottleneck, your access patterns will likely be faster with SSD - because peak throughput is not what you're typically doing.



    edit:
    the raptor on USB getting 40 meg peak is about all you can hope for (USB bus saturated). hook it up to firewire and you'll likely hit 80 meg / sec (firewire saturated). a raptor on anything other than thunderbolt (or SATA) will be bottlenecked by the bus.

    Your macbook should have a SATA2 bus in it, which can do 3gigabit. So, up to 300 meg per second, in theory... you aren't currently bottlenecked by the bus.
     

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