[1300] in RedHat Linux List
RE:Use of dd to copy a drive
daemon@ATHENA.MIT.EDU (Paul Anderson)
Sun Oct 27 15:34:17 1996
Date: Sun, 27 Oct 1996 15:48:31 -0500
From: Paul Anderson <andersop@agapesystems.com>
To: redhat-list@redhat.com
Resent-From: redhat-list@redhat.com
Reply-To: redhat-list@redhat.com
On Sun, 27 Oct 1996, William T Wilson wrote:
"The problem with dd is that the two drives (and the two partitions)
have
to have exactly the same geometry else it will not only not work but
corrupt your destination drive and cause you to have to reformat it.
And
nothing else can write to the drive while this is going on, either, or
random data-corruption type things will happen. It is generally best
not
to rewrite the underlying filesystem. Although the "find" method
proposed
is complex, at least it's safe... (though the "tar" method and cp -a are
safe and easy). "
This statement is inaccurate. The drives do not need to be the same
size and have the exact same geometry. dd is a copy at the bit level
and will simply pick a bit up at one location and write it at another,
which is specified as an arguement. In doing this it does copy *ALL*
the filesystem, including the superblock. Therefore, if you are to copy
the superblock the partitions will have to be the same or the superblock
will have to be edited. Using cp one is not going to copy the files in
the /dev directory or any other special files for that matter. cpio
will not live through soft read write errors, so as long as the transfer
is completely error free you might be OK.
Paul Anderson
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