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I've seen this question on how to backup an SD-card. It's the same solution I would come up with myself; that is basically:

dd if=/dev/blabla of=/home/user/some_file.img`

But my question is if using the argument bs=1M makes any difference. It does when I'm writing to the card, so I suppose it does when I'm reading from it. Is my assumption correct? In the question I referred to earlier, it differs in different answers.

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up vote 4 down vote accepted

From Wikipedia:

A block is a unit measuring the number of bytes that are read, written, or converted at one time.


For some uses of the dd command, block size may have an effect on performance. For example, when recovering data from a hard disk, a small block size will generally cause the most bytes to be recovered. For greater speed during copy operations, a larger block size may be used. When dd is used for network transfers, the block size may have an impact on packet size, depending on the network protocol used.

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Oh! I suppose this site has a rule of not writing stuff like RTFM, but am I allowed to say that to myself? :-p – Niclas Nilsson Nov 26 '12 at 20:15
@NiclasNilsson It's fine. Sometimes we all need to be pointed in the right direction. And lots of people will learn something extra (myself included). – Jivings Nov 26 '12 at 20:23

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