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Re: Cloning 2TB drive

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On Tue, 26 Nov 2024 21:29:03 -0500
Paul <nospam@needed.invalid> wrote:

> On Tue, 11/26/2024 3:32 PM, pinnerite wrote:
> > I am in the process of cloning a 2TB hard drive.
> > I am using this command line:
> > 
> > # dd if=/dev/sda of=/dev/sdb bs=16384 status=progress
> > 
> > I  have been doing this for years.
> > 
> > What struck me as I could see that 1.7TB had been copied, is that a
> > speed of 89Mb/s seems very slow.
> > 
> > This machine does have slowish processor (Intel core i3 about 5 years
> > old) but can I improve on the speed in any way?
> > 
> > 
> 
> The speed of a hard drive, varies 2:1, from outside diameter to hub diameter.
> 
> If the speed near the hub is 90MB/sec, the speed on the outer
> diameter at the beginning of the transfer (when you were not measuring the speed),
> is 180MB/sec.
> 
>    [Picture]   Hard disk drive speed, from one end to the other, showing effects of diameter
> 
>     https://i.postimg.cc/L5HgVBQn/HDTune-31-WD1003-FZEX-00-K3-C.png
> 
> Which is pretty decent.
> 
> The command should have been:
> 
>   sudo dd if=/dev/sda of=/dev/sdb bs=8192 status=progress
> 
> as 8192 always divides evenly into the HDD size. You can use
> FDISK to list the drive characteristics, and there should
> be an overall size parameter to work with. The nice thing about
> modern drives that divide by 8192, is the tagged queuing and
> caching, allows a very high "command rate" delivered from
> dd to the disk(s), and the full transfer rate of the disk
> can be sustained with a block size as low as 8192.
> 
> Linux provides the factor command.
> 
>    factor 12345678      # Factor the drive size, and 8192 as a bunch of 2's as in 2^13 , should be apparent
> 
> If you had told us the model number of the hard drive(s),
> we could then comment on whether the speed number seems low
> or not. To me, if that is the speed near the hub, that
> drive is fine.
> 
> If you purchase a 22TB HDD today, those are ~300MB/sec
> on the outer diameter and ~150MB/sec near the hub. That's
> about as good as it gets. The last time we saw ~300MB/sec
> from a hard drive, it was for a 15K RPM drive from a
> server room. Now, we get that speed on one of the pig drives.
> The smaller drives, a WD Black 500GB, those might be closer
> to your numbers.
> 
>    Paul

Thank you for the above, I have saved it for future reference.

Alan

-- 
Linux Mint 21.3 kernel version 5.15.0-126-generic Cinnamon 6.0.4
AMD Ryzen 7 7700, Radeon RX 6600, 32GB DDR5, 1TB SSD, 2TB Barracuda

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Cloning 2TB drive pinnerite <pinnerite@gmail.com> - 2024-11-26 20:32 +0000
  Re: Cloning 2TB drive Paul <nospam@needed.invalid> - 2024-11-26 21:29 -0500
    Re: Cloning 2TB drive pinnerite <pinnerite@gmail.com> - 2024-11-27 19:20 +0000
  Re: Cloning 2TB drive Jack Strangio  <jackstrangio@yahoo.com> - 2024-12-07 09:35 +0000

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