Questions about the dd command
rebehn at ant.uni-bremen.de
Fri Feb 29 16:40:27 UTC 2008
> I've spent literally hours trying to find direct answers on the dozens
> of websites that discuss 'dd'
> but the couldn't find what I wanted.
> A few questions about the ' dd ' command:
> For example: sudo dd if=/dev/sda2 of=/dev/sdb2 bs=1440
> 1. Which is preferrable; execute the command from an installed
> ubuntu (/dev/sda2) or from a ubuntu CD?
> 2. How do you modify the example to show the data as it is being
> Would this have a drastic effect on how long it takes to complete
> the copy
> compared to just watching a blinking cursor?
> 3. What effect on the does the ' bs = ' number have on
> the time to complete the copy or the accuracy of the copy? Is
> there a
> default number if the the bs= is omitted from the command?
1. You should not use dd to copy a filesystem that is currently mounted,
because parts of it may be cached in RAM. The copy would be
inconsistent. So you better boot from a ubuntu CD.
2. Standard dd does not have a "progress bar" option. However, it will
report its progress when sent a SIGHUP.
3. I don't know, make measurements yourself. 1440 is a somewhat strange
value, use a multiple of 512 (The standard blocksize)
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