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I set up dd to clone a smaller system 40.00GB hard drive (/dev/sda) to a new bigger 111.00GB one connected via a USB reader (dev/sdb) and Its been going for two hours now. The activity meter on the new hard drive shows it's doing something. But the CPU is only about 20%. When is this thing going to complete? Should I re-start the process?

αғsнιη
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    dd is silent so when doing it the first time it seems to take forever. But just be patient. The 'unix way' is that unless it complains it is probably working. Check out this answer for details: https://askubuntu.com/questions/435694/can-i-dd-a-larger-drive-to-a-smaller-one/936556#936556 – SDsolar Aug 13 '17 at 16:46

5 Answers5

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In the future, you should use pv to get a running progress bar.

sudo apt-get install pv

With pv installed, let's assume you want to clone a 20GB drive, /dev/foo, to another drive (20GB or larger!), /dev/baz:

sudo dd if=/dev/foo bs=4M | pv -s 20G | sudo dd of=/dev/baz bs=4M

Important bits to notice: the bs=4M argument sets the blocksize for dd operations to 4MB, which drastically improves the speed of the whole thing. And the -s 20G argument tells pv how big this operation is expected to be, so it can give you an ETA as well as a current speed.

I love pv so hard it should probably be illegal.

Note that while doing it this way is intuitive and nice and neat from left to right ordering, piping to and from STDOUT can incur a performance penalty if you're talking about really fast data streams. The following syntax is faster, if you're looking at moving several hundred MB/sec:

pv -s 20G < /dev/foo > /dev/baz

The -s 20G is optional, if you actually know how big (or about how big) the stream will be, it allows pv to give you a time estimate for completion. Without that, pv will try to figure out how large the dataset is if possible (for instance, it knows how big a file is) but if it can't (eg with a block device, not a file), it just tells you the rate of transfer without guessing how long things will take.

Jim Salter
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    If course, pv is very useful, but if you are copying a lot of data it adds more context switches and buffer copies so it will consume more CPU and perhaps may slow things down a small amount. But since copying data is rate limited on the drives it won't add much overhead. – Colin Ian King Nov 23 '12 at 22:32
  • In actual practice, you are VANISHINGLY unlikely to see pv add so much as 0.1% to the time-to-copy. If you do, it's almost certainly an operation so blindingly fast that there was no point in trying to add a progress bar in the first place. – Jim Salter Nov 23 '12 at 22:34
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    Very true. I'm just and old style engineer who is just used to saving every cycle I can. – Colin Ian King Nov 24 '12 at 14:43
  • @ColinIanKing - I actually just discovered today that while pv itself doesn't slow things down any, piping to STDOUT and STDIN can. For normal dd operations from one conventional hard drive to another, it won't have any impact... but if you have a VERY high performance SSD, it will. My new Intel 520 480GB SSD is capable of 340MB/sec contiguous reads or so, but if I pipe like dd if=/dev/sda bs=4M | dd of=/dev/null bs=4M it only does 276MB/sec or so. Sadface. (The effect is even nastier for cached reads, which may go as fast as 16GB/sec if not piped.) – Jim Salter Nov 26 '12 at 04:55
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    revisiting this later yet: after some conversation with the author of pv, I discovered that you can avoid the speed penalty by taking dd out of the equation entirely: pv < /dev/sda > /dev/sdb works just fine, and will go every bit as fast as the underlying hardware is capable of going. – Jim Salter Aug 10 '13 at 16:54
  • Thanks @JimSalter I was just noticing that my piping: dd if=/dev/sda | pv | dd of=/file was using up 20%, 60%, and 20% CPU respectively. Which to me seems to be a problem. – isaaclw Apr 23 '14 at 01:27
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    dd: bs: illegal numeric value so I went with bs=32m – Jacksonkr Mar 23 '16 at 19:06
  • @JimSalter you should definitely add your comment to your answer, because comments tend to get deleted a lot, thanks – Shayan Oct 24 '19 at 21:55
  • Mac users: pv can be installed using Homebrew, brew install pv. As mentioned in prev comments M is an illegal numeric value, so use m instead, e.g. 4m. – Martin Dec 23 '21 at 10:34
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You can see how far it has got by sending it a SIGUSR1 signal in order to see how much data it has copied and the transfer rate:

kill -SIGUSR1 $(pidof dd)

For copying activity you are limited by I/O speed of the device, so the CPU should not be fully loaded, so don't worry about that.

tshepang
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Colin Ian King
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    Noted. Well, I killed the process to figure out it was going quite slowly.. had to redo the partition table but it's back to all empty now. You know of any better ways to clone a hard drive the won't take all day? –  Nov 22 '12 at 18:28
  • @SeanWebber: running that command should not actually terminate the dd process. From man dd: "Sending a USR1 signal to a running dd process makes it print I/O statistics to standard error and then resume copying." To speed up the process try specifying a larger block size as Jim Salter suggests in the other answer. – Sergey Nov 23 '12 at 00:31
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    OS X's dd must be broken since sending the SIGUSR1 killed it for me as well. – Jarrod Davis Feb 08 '14 at 20:59
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    From elsewhere: kill -INFO $(pgrep ^dd$) on BSD systems (like OSX). – ThatOneDude Jan 11 '16 at 22:57
  • There's an easier way to get progress output from dd now. See may answer! – Elder Geek Feb 28 '17 at 18:20
  • Will this kill the process? – tjespe May 11 '17 at 11:07
  • No, the SIGUSR1 is handled by dd and it won't kill it at all. Only SIGKILL, SIGHUP etc will kill it. – Colin Ian King May 11 '17 at 18:42
  • I just did this and it does not kill the process. Here is example output: 10712217+0 records in [newline] 10712217+0 records out [newline] 5484655104 bytes (5.5 GB, 5.1 GiB) copied, 2233.64 s, 2.5 MB/s – pauljohn32 Jan 19 '20 at 17:25
  • I love this because it doesn't required you to start copying from scratch to see the progress. – dawid Feb 16 '21 at 18:18
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I've used pv as well as (ps and kill) in the past as suggested in the other answers, but more recently I've just been using dc3dd instead which produces the same results while providing a progress report throughout the process.

You can check to see if it's already installed with: which dc3dd

If not you can install it with sudo apt-get install dc3dd

The command switches are similar to dd (for cloning, although wiping is a bit more straightforward).

In your case I would use the command dc3dd if=/dev/sda of=/dev/sdb

Edit:

Recent versions of dd from the coreutils package version 8.24+ included in Ubuntu 16.04 and later include a status parameter. You can accomplish the same result with dd by adding the status=progress switch to your dd command line.

Example: dd if=/dev/zero of=/dev/null count=1000 status=progress

Elder Geek
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I had a similar problem. The cause was different in my case.

The target drive is an external hard disk.

If the disk was mounted automatically via udisks and udisks-glue then the transfer rate from cdrom to the hd was about 40kB/s.

When I unmounted the hd and mounted it directly via mount I got a transfer rate of about 2.4MB/s.

Tobias
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You could instead use ddrescue:

sudo ddrescue -v /dev/sda /dev/sdb

v stands for verbose.

atmelino
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