Date: Sat, 01 Dec 2007 14:19:59 -0600 From: Kevin Kinsey <kdk@daleco.biz> To: stevefranks@ieee.org Cc: User Questions <freebsd-questions@freebsd.org> Subject: Re: using dd to duplicate disks/partitions of slightly different sizes - works? Message-ID: <4751C1EF.4010206@daleco.biz> In-Reply-To: <539c60b90712010929m7fef7020v806eb3c1eb24d066@mail.gmail.com> References: <539c60b90712010929m7fef7020v806eb3c1eb24d066@mail.gmail.com>
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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
> ok?
>
> The other option is just to fdisk & label the other disk, then rsync
> everything to it. Is that the wiser choice?
>
> Thanks,
> Steve
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
McCormack):
-----------------------------------------------
>> 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 :)
------------------------------------------
HTH,
Kevin Kinsey
--
There is no royal road to geometry.
-- Euclid
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