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bug#7362: dd strangeness

From: Pádraig Brady
Subject: bug#7362: dd strangeness
Date: Wed, 10 Nov 2010 15:29:41 +0000
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100227 Thunderbird/3.0.3

On 10/11/10 10:22, Lucia Rotger wrote:
> I see this behavior in Solaris, Linux and BSD dd: if I send a big enough
> file they all read it short at the end of the stream.
> This works as expected:
> # cat /dev/zero | dd bs=512 count=293601280 | wc
> I get the expected results, dd reads exactly 293601280 blocks and wc
> sees 150323855360 characters, 140 GB
> Whereas substituting cat for zfs send doesn't:
> # zfs send <backup> | dd bs=512 count=293601280 | wc

different write sizes to the pipe mean
in the later case, dd will get short reads.
IMHO dd is doing the wrong/most surprising thing here,
but it can't be changed for compatibility reasons.
You can get coreutils dd to do what you want with:

dd iflag=fullblock


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