Mac Pro SATA copying speeds seem too slow

Discussion in 'Mac Pro' started by clamnectar, May 7, 2009.

  1. macrumors regular

    Joined:
    May 7, 2009
    #1
    Based on what I've read about SATA, my Western Digital 1 TB Black Caviar drives should be able to read and write faster than 50 MB/sec. But that's the best I've gotten from anything. I thought I could expect 300 MB/sec, or 150 at the very least. What's the deal? This is a 2008 8 core 2.8 Mac Pro, by the way.
     
  2. macrumors member

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    Oct 9, 2007
    #2
  3. macrumors 601

    Tesselator

    Joined:
    Jan 9, 2008
    Location:
    Japan
    #3
    Well, there's various speeds a typical drive can deliver:

    Sustained I/O
    Burst I/O
    Cache I/O
    Random I/O

    Copying many small files from one drive to another is an example of Random I/O - Usually about 5 ~ 50 MB/s.
    Copying a large file or loading one is an example of Sustained I/O - Usually 70 ~ 120 MB/s
    Cache I/O is reading or loading anything already in the drive's cache - can be as high as 2 GB/s (mine typically hits 1.3 ~ 2 GB/s)
    And I'm not too sure when or why burst kicks in nor what speeds are achieved - others might know.

    There are I/O accelerators but I don't think Mac OS X supports them. They're usually around 500 GB or less (optionally battery backed) and have their own processor. It's a bit like adding a massive L2 cache to the SAS or SATA bus.
     
  4. macrumors newbie

    Joined:
    Mar 25, 2009
    #4
    50 sounds about right for a single drive. It's unlikely to give you 150 mb/s sustained transfer in real world apps. I only get about 150 mb/s on a 3 drive RAID 0 array.
     
  5. macrumors 601

    Tesselator

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    #5
    Wow! That's pretty bad! I'm getting between 250 MB/s and 400 MB/s tho usually on the lower end. (3 Drive RAID 0)
     
  6. thread starter macrumors regular

    Joined:
    May 7, 2009
    #6
    this is time machine backing up / duplicating a single 4 GB file. From the sounds of it, I'm not too far off the curve, so I guess everything's working correctly.
     
  7. macrumors P6

    DoFoT9

    Joined:
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    Location:
    Singapore
    #7
    my iMac gets 80MB sustained read/write, no RAID. does that count?? :p

    well there you have it. you can't go off Time machine benchmarks because it runs REALLY really slowly (has to update the database, runs as a lower priority task blaablaa). copy a large file to another folder or something and see how you go.
     
  8. thread starter macrumors regular

    Joined:
    May 7, 2009
    #8
    duplicating a 4 gigabyte file: zigzagging between 60 MB/sec and 40 MB/sec, as measured by activity monitor. the graph looks like a mountain range. duplicated the same file three times, always the same speed.
     
  9. macrumors 6502

    Joined:
    Nov 18, 2008
    Location:
    Denver, CO
    #9
    So, I just want to understand the question. Your assumption was that the hard drive you purchased would preform better in a mac pro than it would in test machines that yielded 50MB/sec, and you want to know "what gives"?

    Also the numbers you mention 300MB/s and 150 sound suspiciously like you're anticipating your drive throughput to be a direct product of the SATA bandwidth.
     
  10. macrumors P6

    DoFoT9

    Joined:
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    #10
    my guess is because its is copying to the same HD, has to work a lot harder.. maybe try to copy to another disk/external drive?
     
  11. macrumors 601

    Tesselator

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    #11
    Yeah, I think that's about right for "duplicating" a file on the same HDD.

    Knowing BSD tho I bet there's a system variable hiding out somewhere that will allow the buffer size to be increased. This might speed it up a bit. Maybe zig-zag between 60 and 90 MB/s or something. :D Also a file that size and you can time it pretty accurately with a stopwatch.
     
  12. thread starter macrumors regular

    Joined:
    May 7, 2009
    #12
    you're indeed right. i'm not sure why i didn't think of it, but duplicating is slower because the drive heads are reading and writing. copying that same 4 gig file to one of the other drives gives me 100 MB/sec. definitely a solid speed.

    thanks for clearing up some of my misconceptions.
     
  13. macrumors 68000

    Joined:
    Sep 12, 2007
    #13
    I managed to get 105Mb/sec between two WD Blacks 1TB.

    They were totally empty, I was seeing how quick I could get them :p

    12Gb H264 file, peaked at 106.4, min at like 87 towards the end.

    Blazing fast!

    Even managed to get 66Mb/sec across Gigabit :D
     
  14. macrumors 601

    Tesselator

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    #14
    Kewl! Data type also matters as I believe all HDDs these days are RLE. RLE is a kind of compression. So for example if you're doing that with a 12GB uncompressed AVI of nothing but a solid color it should be considerably faster than if your 12GB AVI is of already compressed data or contains temporal deltoid change. :)
     

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