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Speed of 'dd' vs. Disk Utility

 
 
Wes Groleau
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      12-27-2011, 03:24 AM
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
 
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Wes Groleau
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      12-27-2011, 04:46 AM
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.
 
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Andreas Rutishauser
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      12-27-2011, 05:36 AM
Salut Wes

In article <jdbdpu$er9$(E-Mail Removed)>,
Wes Groleau <(E-Mail Removed)> 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
<(E-Mail Removed)>, Fon: 044 / 721 36 47
 
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David Empson
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      12-27-2011, 06:00 AM
Wes Groleau <(E-Mail Removed)> 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
(E-Mail Removed)
 
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Wes Groleau
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      12-27-2011, 06:20 AM
On 12-27-2011 00:36, Andreas Rutishauser wrote:
> Wes Groleau<(E-Mail Removed)> 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)
 
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Wes Groleau
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      12-27-2011, 06:21 AM
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
 
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Király
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      12-27-2011, 08:23 AM
Wes Groleau <(E-Mail Removed)> 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.
 
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Paul Sture
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      12-27-2011, 08:46 AM
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
 
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