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Re: dd effect on cloning of iso file to usb stick


From: jb
Subject: Re: dd effect on cloning of iso file to usb stick
Date: Fri, 3 Oct 2014 10:56:31 +0000 (UTC)
User-agent: Loom/3.14 (http://gmane.org/)

Bernhard Voelker <address@hidden> writes:

> ... 
> > $ lsblk -f
> > ...
> > sdb    iso9660 ARCH_201410 2014-10-01-05-00-04-00
> > ├─sdb1 iso9660 ARCH_201410 2014-10-01-05-00-04-00
> > └─sdb2 vfat    ARCHISO_EFI A05B-32C8
> > ...
> >
> > # fdisk -l /dev/sdb
> > ...
> > Device     Boot Start     End Sectors  Size Id Type
> > /dev/sdb1  *        0 1171455 1171456  572M  0 Empty
> > /dev/sdb2         252   63739   63488   31M ef EFI (FAT-12/16/32)
> ... 

>    $ fdisk -l Downloads/archlinux-2014.10.01-dual.iso

Device                                   Boot Start     End Sectors  Size Id
Type
Downloads/archlinux-2014.10.01-dual.iso1 *        0 1171455 1171456  572M  0
Empty
Downloads/archlinux-2014.10.01-dual.iso2        252   63739   63488   31M ef
EFI (FAT-12/16/32)

> ... 
> For dd(1), it's all just data - byte per byte.
> It's the interpretation of the data that makes the difference.
> The kernel e.g. has to check if there's a partition table at the
> beginning of a device, /dev/sdb in this case, and indeed there is one.
> Therefore, it provides access to the partitions as sdb{1,2}.
> ...

Yes, indeed, I confused dd operation with its results as interpreted by
other tools (fdisk, etc) and presented to the user.

W/r to that interpretation, in a dos (MBR) partitioning scheme, the hard
disk can contain at most four primary partitions, or alternatively
three primary partitions and an extended partition.
The only way to have embedded (logical) partitions is thru dedication of
one primary partition to an extended partition mechanism.
What the fdisk shows here, at least start/end sectorwise, is that sdb2
partition is physically embedded in sdb1 partition.
So, how to interpret sdb1 and sdb2 partitions (primary, extended,
logical) ?
Is this a case of extended partition mechanism ?

jb





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