Steve Franks wrote:
I've got two 160GB disks.  Different manufacturers, so different #
bytes.  One is FreeBSD, the other blank.  I'd like to backup my system
for the fastest possible recovery after a crash - move the plug and
power up.  I have gmirrored before, but I just wanted to do a quick
dd, since I don't want to abuse my cheapo powersupply (has 4 disks
already on it).

Two questions:

(1) If I dd from the smaller to the larger, will it work?  What
happens to the extra, say 5MB of unused space - will my partition info
be messed up?

(2) If I dd from the larger to the smaller (df reports only 50% used
anyway) is there a way to make sure there is no info in the 5MB at the
end that will overflow the smaller, and again, will my partitions be

The other option is just to fdisk & label the other disk, then rsync
everything to it.  Is that the wiser choice?


Giorgos Keramidas made a great post dealing with this
a while back.  Here 'tis, quoted for your enjoyment
and potential enlightenment (also quoted is Martin

     It turns out that dd defaults to 512-byte blocks so I didn't
really need the bs=512, but I am not sure I haven't made some other
type of mistake.  The dd command has been running for about 4 hours on
a very fast system, with a 1-gig processor, 1 gig of RAM and two 31-GB
drives.  One would think it should have finished by now, but it is
still running.  Is this a valid method of copying the entire contents
of one drive to another?  Thank you.

Bah!  That's too slow for my taste.  I would usually go for a newfs,
dump, and restore option.  For instance, to create a copy of /usr on a
second disk:

   newfs -U /dev/ad1s1a
   mount /dev/ad1s1a /mnt
   dump -0 -a -L /usr | ( cd /mnt ; restore ruvf - )

Copying with dd(1) is not as fast  :)

Kevin Kinsey
There is no royal road to geometry.
                -- Euclid
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