Hard Drive bandwidth

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

  1. softwareguy256 macrumors regular

    Jun 5, 2010
    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

    Nov 28, 2010
    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


    Jan 24, 2010
    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 68020

    Oct 28, 2006
    Alice, TX
    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 603


    Feb 13, 2012
    Perth, Western Australia
    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.

    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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