[RDD] Redundant Hard Drive/Backup

Cowboy curt at cwf1.com
Wed Jan 8 16:15:02 EST 2014

On Wednesday 08 January 2014 03:17:42 pm Cowboy wrote:
>  dd is not a good idea.
>  dd can destroy your data in one bit.

 Just to elaborate a little...

 dd is (D)evice to (D)evice.
 Doesn't matter what that device is, or isn't.
 Want to copy your monitor display over your partition tables,
 pixel for pixel ? dd is your tool.
 Want to write your boot block to your modem ?
 Again, dd is the tool.
 Want to copy an entire disk, including boot block, partition tables,
 geometry representations, and data, bit for bit into a file ?
 Again, dd is your tool.
 Yes, Virginia, you can create a bootable text file, and dd will do it.

 Want to copy one file to another file ?
 dd is not the best tool in the box for that.

 cp is quick, and simple, but limited.
 rsync can do everything cp can do, and much more, but it can't
 do the kinds of things dd can do.
 Can dd copy files ?
 Yes, it can, if you give it the correct command options and in the
 correct order.
 Whatever command options you don't give it, it will assume some
 defaults, like byte offset, or block size, what to do when an error
 is encountered..... ( which is stop dead in it's tracks. Do not back out,
 and make no attempt to recover. Just stop )
 If you tell it to copy a file, will it check first to make sure that the
 file you're copying actually is a file, or is locked by some other process ?
 NO !
 It will blindly copy whatever it thinks you've told it, and that's where
 it can get you into trouble.
 A file that is currently being updated, dd will likely create trash at the
 target, where neither cp nor rsync will do that.



You're never too old to become younger.
		-- Mae West

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