Speed of 'dd' vs. Disk Utility

Discussion in 'Apple' started by Wes Groleau, Dec 27, 2011.

  1. Wes Groleau

    Wes Groleau Guest

    Using Disk Utility to clone my backup drive.

    Says it has four hours to go, less than half done.

    450 GB on USB. Each drive on a different port.

    Even if each uses 200 MBps instead of the alleged
    480 MBps max, wouldn't it still be less than 3600 seconds?

    Would it be worthwhile to kill it and start over with 'dd' ?

    If they weren't SATA drives, I could have stuck them inside
    an old Linux box and done them in a few minutes.

    --
    Wes Groleau

    Fossilization … to teachers.
    http://Ideas.Lang-Learn.us/barrett?itemid=1476
     
    Wes Groleau, Dec 27, 2011
    #1
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  2. Wes Groleau

    Wes Groleau Guest

    On 12-26-2011 22:24, Wes Groleau wrote:
    > Even if each uses 200 MBps instead of the alleged
    > 480 MBps max, wouldn't it still be less than 3600 seconds?


    Oops. Thanks! to the semi-nonymous tipster who reminded me
    of the difference between bits and bytes. :)

    It started out predicting two days, but it soon corrected itself
    to six hours and then to five. Five hours for 450 GB is about
    maximum USB 2 speed. And if it has start and stop bits, it's faster
    than advertised.

    --
    Wes Groleau

    Guidelines for judging others:
    1. Don't attribute to malice that which
    can be adequately explained by stupidity.
    2. Don't attribute to stupidity that which
    can be adequately explained by ignorance.
    3. Don't attribute to ignorance that which
    can be adequately explained by misunderstanding.
     
    Wes Groleau, Dec 27, 2011
    #2
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  3. Salut Wes

    In article <jdbdpu$er9$>,
    Wes Groleau <> wrote:

    > Using Disk Utility to clone my backup drive.
    >
    > Says it has four hours to go, less than half done.
    >
    > 450 GB on USB. Each drive on a different port.


    different port ok, but different bus?
    >
    > Even if each uses 200 MBps instead of the alleged
    > 480 MBps max, wouldn't it still be less than 3600 seconds?


    Typical transfer speed on Mac USB 2.0 is 30MB/sec.
    >
    > Would it be worthwhile to kill it and start over with 'dd' ?
    >
    > If they weren't SATA drives, I could have stuck them inside
    > an old Linux box and done them in a few minutes.


    A MacPro is prepared to take up to 4 SATA drives internally...

    Cheers
    Andreas

    --
    MacAndreas Rutishauser, <http://www.MacAndreas.ch>
    EDV-Dienstleistungen, Hard- und Software, Internet und Netzwerk
    Beratung, Unterstuetzung und Schulung
    <mailto:>, Fon: 044 / 721 36 47
     
    Andreas Rutishauser, Dec 27, 2011
    #3
  4. Wes Groleau

    David Empson Guest

    Wes Groleau <> wrote:

    > On 12-26-2011 22:24, Wes Groleau wrote:
    > > Even if each uses 200 MBps instead of the alleged
    > > 480 MBps max, wouldn't it still be less than 3600 seconds?

    >
    > Oops. Thanks! to the semi-nonymous tipster who reminded me
    > of the difference between bits and bytes. :)
    >
    > It started out predicting two days, but it soon corrected itself
    > to six hours and then to five. Five hours for 450 GB is about
    > maximum USB 2 speed. And if it has start and stop bits, it's faster
    > than advertised.


    450 GB in five hours is 25 MB/s (200 Mbps not counting protocol
    overhead). That's within achievable real world throughput for USB 2.0.
    Best I've seen is about 31 MB/s for copying of large blocks of data.

    If Disk Utility is copying files, it will be slower than the theoretical
    limit due to the overhead of copying lots of small files and the
    directory information for each.

    If it is copying sectors it should approach the maximum speed achievable
    via USB for that combination of drives, since it will be able to do
    large transfers.

    I think Disk Utility only does sector copies if the source and
    destination drives are exactly the same size.

    --
    David Empson
     
    David Empson, Dec 27, 2011
    #4
  5. Wes Groleau

    Wes Groleau Guest

    On 12-27-2011 00:36, Andreas Rutishauser wrote:
    > Wes Groleau<> wrote:
    >> If they weren't SATA drives, I could have stuck them inside
    >> an old Linux box and done them in a few minutes.

    >
    > A MacPro is prepared to take up to 4 SATA drives internally...


    If I had a Mac Pro, I wouldn't have bothered to mention the
    old Linux box. Also, one of them is a tower-sized SATA (3.5 inch)

    --
    Wes Groleau

    There ain't no right wing,
    there ain't no left wing.
    There's only you and me and we just disagree.
    (apologies to Jim Krueger)
     
    Wes Groleau, Dec 27, 2011
    #5
  6. Wes Groleau

    Wes Groleau Guest

    On 12-27-2011 01:00, David Empson wrote:
    > If it is copying sectors it should approach the maximum speed achievable
    > via USB for that combination of drives, since it will be able to do
    > large transfers.
    >
    > I think Disk Utility only does sector copies if the source and
    > destination drives are exactly the same size.


    They are not the same size, but it does claim to be "copying blocks"
    and it is estimating close to maximum speed.

    --
    Wes Groleau

    Teacher Tip: Organization
    http://Ideas.Lang-Learn.us/russell?itemid=1568
     
    Wes Groleau, Dec 27, 2011
    #6
  7. Wes Groleau

    Király Guest

    Wes Groleau <> wrote:
    > > I think Disk Utility only does sector copies if the source and
    > > destination drives are exactly the same size.

    >
    > They are not the same size, but it does claim to be "copying blocks"
    > and it is estimating close to maximum speed.


    A sector copy (aka block copy) is possible if the destination volume is
    equal to or larger than the source volume.

    Block copies copy everything, including free space, so if the drive has
    a lot of empty space on it, a file level copy (like with SuperDuper)
    will be faster.

    --
    K.

    Lang may your lum reek.
     
    Király, Dec 27, 2011
    #7
  8. Wes Groleau

    Paul Sture Guest

    On Mon, 26 Dec 2011 23:46:17 -0500, Wes Groleau wrote:

    > On 12-26-2011 22:24, Wes Groleau wrote:
    >> Even if each uses 200 MBps instead of the alleged 480 MBps max,
    >> wouldn't it still be less than 3600 seconds?

    >
    > Oops. Thanks! to the semi-nonymous tipster who reminded me of the
    > difference between bits and bytes. :)
    >
    > It started out predicting two days, but it soon corrected itself to six
    > hours and then to five. Five hours for 450 GB is about maximum USB 2
    > speed. And if it has start and stop bits, it's faster than advertised.


    My rule of thumb for large transfers to USB 2 drives is ~100GB per hour,
    so that sounds about right.



    --
    Paul Sture
     
    Paul Sture, Dec 27, 2011
    #8
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