Re: Can dd cross device boundaries?

[Francois Marier]

On 2012-01-09 at 09:42:17, Pádraig Brady wrote:
> Highly unlikely.
> If so it would be a kernel bug, but it's almost certain that is not what 
> happened.
> disk enumeration is often quite complex.
> Did you reboot after the wipe? Perhaps the disks are now swapped because
> of your wiping operation?

What was really strange and can't explain is that everything started failing
on /dev/sdb after the wipe of /dev/sda completed successfully. For example,
running "top" or cat'ing a file would fail with "Input/Output Error". Which
is why I started to suspect that perhaps the dd operation has jumped to the
other device. Then it stopped booting after I power-cycled it.

Anyways, it sounds like it's unrelated (maybe a loose cable or something). I
will investigate further once I get the drives (it was in a remote server
which I can no longer ssh into).

> p.s. There is no need to specify count if write to the whole device.
> Also bs=1M might be faster.

That's good to know. So I guess I should have done this:

  dd if=/dev/zero of=/dev/sda bs=1M

What's the expected behavior if a dd command causes dd to attempt to write
past the end of the drive (I'm thinking that maybe I got my math wrong)? It
just stops with an error of some sort?

Cheers,
Francois

-- 
Francois Marier                         identi.ca/fmarier
http://fmarier.org                    twitter.com/fmarier