GNU bug report logs - #8171
[dd] bs=blocksize doesn't work as expected

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Message #8 received at 8171 <at> debbugs.gnu.org (full text, mbox):

From: Ondrej Vasik <ovasik <at> redhat.com>
To: Станислав
	<ginermail <at> gmail.com>
Cc: 8171 <at> debbugs.gnu.org
Subject: Re: bug#8171: [dd] bs=blocksize doesn't work as expected
Date: Fri, 04 Mar 2011 14:30:38 +0100

On Fri, 2011-03-04 at 08:02 +0300, Станислав wrote:
> [dd] bs=blocksize doesn't work as expected, for example:
> tar -c /somedir | dd bs=256K of=/dev/nst0
> In this example backup record will be recorded to a tape with block size =
> 10K instead of 256K because 10K is default for tar.
> There is workaround:
> tar -c /somedir | dd ibs=256K obs=256K of=/dev/nst0
> If we set block size for input and output separatly - it works as expected.

Even partial block (short read) is a block - especially when you read
via pipe. If you want to have only fullblock, dd provides
iflag=fullblock for you. See info documentation (or online GNU coreutils
manual) for details.

> lucid <http://packages.ubuntu.com/lucid/coreutils> (utils): The GNU core
> utilities
> 7.4-2ubuntu2: amd64 i386

Current version is 8.10, but iflag=fullblock should be present there -
added in 7.0

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