LinuxSA Mailing list archives

  From: Alan Kennington <akenning@topology.org>
  To  : LinuxSA <linuxsa@linuxsa.org.au>
  Date: Thu, 28 Jun 2001 22:09:04 +0930

Re: dd time frame

On Thu, Jun 28, 2001 at 11:50:33AM +0000, wlsimes@tell.net.au wrote:
> 
> I have an old Pentium 166mhz with 64mb ram in which I am performing a 
> dd if=/dev/hda of=/dev/hdc  between 2 x 30gb IDE hard drives. This is 
> being done while in multiuser mode, I suspect that there would also 
> be a small amount of network activity, e-mails coming and going would 
> be about the limit though.
> 
> It's been slugging away now for at least three hours, this seems a 
> bit long, but on the other hand being ide and only a P166 it could be 
> on track, I am not sure. There is nothing in any log files to 
> indicate and problems.

I am not an expert, but... I think the chances that you get a 
self-consistent file system out of "dd" used over 3 hours with
a machine that's in use are rather low.
"dd" makes a linear scan, which would, I think, probably read in
the inodes first, and then the data blocks etc.
You're going to end up with all kinds of inconsistencies - probably
much worse than if you turned off your machine's power
during some serious activity.

The dump/restore programs seem to be remarkably resilient in the
face of continuing activity because of the way the dump program
organises its copying.
But if you want a precise file system snapshot, not just getting
all the files correct, then you will have to mount the file
system to be copied in read-only mode.
Anything else, as I say, should give you something at least
as nasty, if not worse, than a sudden loss of power would give you.
It woudl be more like 3 hours of power losses.

I hope the experts will correct me if I'm wrong.

> Does anyone think there is a problem and that I should kill it and 
> redo this is single user mode ?

Personally, I'd kill the job and try something that has a
reasonable probability of success.

> I have looked at the man pages for verbose output, but there doesn't 
> seem to be an option for it. Am I overlooking it or is there another 
> way ?

I don't think you'll get anything useful from "dd" output.
It's just a block copier. As long as there are blocks to be copied,
it won't care less what's in them.

Cheers,
Alan Kennington.

-- 
LinuxSA WWW: http://www.linuxsa.org.au/  IRC: #linuxsa on irc.linux.org.au
To unsubscribe from the LinuxSA list:
  mail linuxsa-request@linuxsa.org.au with "unsubscribe" as the subject