raw disk copying?

Jules Richardson julesrichardsonuk at yahoo.co.uk
Tue Apr 25 21:33:14 CDT 2006

Michael B. Brutman wrote:
>> My first experiment was with linux where I created a PC linux
>> boot CD and hooked my two drives up planning to just dd from
>> one drive's raw device to the other. To my amazement, I discovered
>> that linux does not have a raw disk I/O capability by default.
>> I tried using the block devices, but the resulting copy was
>> not intact. After doing a bit of searching, I discovered that
>> there is some sort of rawio extension which allows a raw device
>> to be associated with a block device, but it also said that dd
>> would not work with this raw device due to buffer alignment
>> issues vs. DMA. Go figure...
> I missed something here ..  why didn't dd work for you? 

That was my initial thought, that I must be missing something - but I guess 
the original poster is trying to copy across non-identical drives, with 
filesystems containing data which addresses the disk by something other than 
linear blocks. I'm betting then that a raw copy wouldn't work because the 
target drive's geometry is totally different.

To identical drives, *or* when the copied data is a filesystem that addresses 
by linear block from the start of the filesystem, I can't see any reason why 
dd won't work.



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