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Date: Mon, 18 Apr 2016 16:21:26 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: "Kevin P. Neal" <kpn@neutralgood.org>
cc: freebsd-questions@freebsd.org
Subject: Re:  tool for mapping away bad blocks on an external disk
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On Mon, 18 Apr 2016, Kevin P. Neal wrote:

> On Mon, Apr 18, 2016 at 08:55:34AM +0200, Matthias Apitz wrote:
>>
>> Thanks for all the hints; I started last night with overwriting the full
>> disk with:
>>
>> # dd conv=noerror if=/dev/zero of=/dev/da0 bs=1m
>
> Just curious: Does anyone know what happens when there is not enough space
> at the end of a disk (or tape) to write the entire block? Does a partial
> block get written, or does no block get written?

It writes the partial block.  Or at least I've never bothered doing 
anything special, and the checksums work out.

> It is because I don't know what happens that I usually pick a block size
> that is mathematically factored out from the number of blocks on the disk
> (and then multiplied by the number of bytes in a block obviously).

You work too hard. :)