USB3.0 external drive 120Mb/s?

Discussion in 'iMac' started by imacken, Nov 19, 2015.

  1. imacken macrumors 65816

    Feb 28, 2010
    When I run BlackMagic Disk Speed Test on my Samsung D3 external USB3.0 drive, I get read and write speeds of 120Mb/s! My iMac late 2015 supports USB3.0, so why should that be?
  2. Jimios macrumors member


    Nov 7, 2015
    This is a pretty normal speed for a HDD, especially if it's 5400rpm. Your speed in this case is limited by the HDD rather than the interface.
  3. Samuelsan2001 macrumors 604

    Oct 24, 2013
    Because thats how fast HDD's are (well 5400rpm ones anyway the 7200rpm run to about 180Mb/s).
  4. imacken thread starter macrumors 65816

    Feb 28, 2010
    Thanks for your help. Supposedly a 7200 in the Samsung, but.....
  5. tyche macrumors 6502

    Jul 30, 2010
    115-120Mb/s is fast. That's already showing 7200 rpm disk speeds. That's why SSD and especially pcie versions are so awesome.
  6. m85476585 macrumors 65816

    Feb 26, 2008
    The speed depends more on the density of data on the platters than on the spin speed. A 1TB 5400RPM disk will be much faster than something like a 160GB 7200RPM disk. Random seek might take slightly longer on the 5400 RPM drive.

    120MB/sec is fast for a spinning disk. A few years ago (maybe around 2010), people couldn't even comprehend that a disk could saturate USB 2.0 (around 35MB/sec) meanwhile my 1TB disks were showing 80-100MB/sec on eSATA. USB3.0 takes away a big bottleneck, but now the disk is the main limitation.
  7. jerwin, Nov 19, 2015
    Last edited: Nov 19, 2015

    jerwin macrumors 68000

    Jun 13, 2015
    That would be awesome for a USB 2.0 drive, which would be limited to 48 MB/s, so it's definitely USB 3.0.

    Still, Blackmagic shows my LaCie Minimus drive (7200 RPM) at 172 MB/190 MB, so perhaps the Samsung D3 isn't on the leading edge of spinning rust. However, this review

    says that 216MB/s and 203MB/s should be possible.

    So there's possibly some other things going on.

    Is it formatted as NTFS? HFS+? Is it encrypted?
  8. imacken thread starter macrumors 65816

    Feb 28, 2010
    Thanks for that. It's formatted as HFS+ and not encrypted.
    The review did say that those speeds were not seen in real-world tests', so, not sure.

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