[CALUG] SSH question

James Ewing Cottrell 3rd JECottrell3 at Comcast.NET
Thu Nov 17 13:43:35 CST 2005

Well, first, you don't stand a chance unless the filesystem is 
unmounted. Second, the partitions that you copy between must be 
identical. Don't forget that the first primary partition starts one 
sector later than the other primaries to make room for the MBR.

Now you *could* copy them to a file or tape for restore later, but then 
you'd have to make sure that you resore them to the same place or 
identically sized partition. You can use a larger one, but you would 
waste space upon restore.

The situation tends to be worse among drives of different geometry. 
Remember that file systems are laid out in cylinder groups.

I would pose the opposite question: why do you want to do this? Any 
speedup you might get are likely to be offset by the pitfalls you are 
likely to encounter.

I have seen a dd fail when by all the above criteria it should have 

It might be useful in certain cases, such as cloning disks or moving 
data from one drive to another, but I would be very careful.

If you do this, run an fsck and make sure the number of files and size 
EXACTLY match. If your really paranoid, run md5sum on them.


Bryan Breen wrote:
> david l goodrich wrote:
>>James Ewing Cottrell 3rd wrote:
>>>Using DD to back up partitions is a Bad Idea! Pick Something Else!!
>>why?  `dd` works just fine depending on what you're trying to do.  i've
>>used it with great success in the past.
>>  --david
> I too am curious to know what is wrong with using dd to copy drive 
> partitions (or the entire drive)?
> - Bryan
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