[Fwd: Re: [SlugBug] Some disk related questions..]

[Chris J]

didnae notice reply-to isn't set to list. *makes mental note*

---------------------------- Original Message ----------------------------
Subject: Re: [SlugBug] Some disk related questions..
From:    "Chris J" <cej at nightwolf.org.uk>
Date:    Thu, August 7, 2003 9:16
To:      Philippe Béchamp <bechamp at web.net>
--------------------------------------------------------------------------


And Lo! The Great Prophet " Philippe Béchamp" uttered these words of wisdom:
>
> Hi all !
>
> * Partition tables are exclusively located in the MBR.
>

Nope. BSD's are the funny one here, as you partition a disk into A, B and
C, but then you use disklabel to then partition further if required. This
caught me out the first time I installed it; had to blow my partitions and
start over. You usually end up creating just *one* physical partition for
BSD, then use disklabel to split that up into logical partitions. As far
as the BIOS is concerned, there's only four partitions, but BSD sees the
four physical ones and all the logical ones. IIRC, the diskalabel is
stored at the start of the parition somewhere.

>
> Does the bs= parameter in 'dd' make any difference to the resulting file
? I think it only changes the way the copy is done, not what is written
??
>

Correct. It is more efficient to choose a suitable block size for the
device you are reading from (or possibly writing too), and thus is usually
a power of 2. For example, reading from CDs would benefit with a BS of
1024, as that is their physical block size. You could also use a multiple
of 1024 - not sure if it gains anything though (experiement there for the
reader).

For example, choosing a block size of, say, 1500 isn't the best choice
because for each read, you have to read two blocks of data, then for the
next read, you read another two blocks - one of which you've read once in
your previous read. Sizing the bs so that it will always read complete
blocks of data (be it one or many) is the way to go.


-- 
\ Chris Johnson                 \
 \ cej at nightwolf.org.uk          \
  \ http://cej.nightwolf.org.uk/  ~-----------------------------------+
   \ Redclaw chat - http://redclaw.org.uk - telnet redclaw.org.uk 2000 \____




-- 
\ Chris Johnson                 \
 \ cej at nightwolf.org.uk          \
  \ http://cej.nightwolf.org.uk/  ~-----------------------------------+
   \ Redclaw chat - http://redclaw.org.uk - telnet redclaw.org.uk 2000 \____