[sclug] dd question

[Pieter Claassen]

The two drives that I am copying are exactly the same on the same
motherboard.

The swap partition might be a problem and I wonder if disabling swapping for
the copy might not be a good idea? Everything should happen in ram anyhow
since the bs is only 4Mb.

I expected that if I make sure that the root partition is only ro and swap
is off that there should not be a problem copying the disk. What happens to
the proc filesystem with a dd?

Pieter
----- Original Message -----
From: "James Fidell" <james at cloud9.co.uk>
To: "Pieter Claassen" <pieter at openauth.co.uk>; <sclug at sclug.org.uk>
Sent: Monday, February 24, 2003 12:35 AM
Subject: Re: [sclug] dd question


> Quoting Rick Payne (rickp at rossfell.co.uk):
> >
> >
> > --On Friday, February 21, 2003 1:26 pm +0000 Pieter Claassen
> > <pieter at openauth.co.uk> wrote:
> >
> > > If I pop the master and slave HD's into a new machine booted from
another
> > > HD, then they copy in about 30 minutes.
> > >
> > > I noticed in both cases that kswapd was going for it, but other than
that
> > > I don't understand the massive time difference.
> >
> > Presumably you had no swap on the first 'dd', so had rather less memory
> > available for caching the read/writes.
>
> And if you are swapping, exactly which device are you swapping to, and
> how will that affect disk-to-disk copy performance?
>
> There are loads of other possibilities, too.  Perhaps the first system
> has very poor IDE performance compared to the second, for any number of
> reasons.  Could be the amount of read-ahead, PIO vs. DMA, other load on
> the IDE bus or even motherboard hardware.  Performance problems can be
> very tricky to track down, especially when you can't compare a "good"
> system against a "bad" system by changing one thing at a time.
>
> James
>
>