increasing dd disk to disk transfer rate

[John Nielsen]

On Friday 13 January 2006 08:29 am, Christoph P. Kukulies wrote:
> On Thu, Jan 12, 2006 at 02:23:37PM -0700, Kenneth D. Merry wrote:
> > > written by phk) that is designed to do disk-to-disk recovery - it
> > > copys data in big slabs until it gets an error and then works around
> > > the faulty area block by block.
> >
> > It's called 'recoverdisk', and is in src/tools/tools/recoverdisk.
> >
> > I used it to copy a friend's hard drive, and it worked well.  (Although
> > the supposedly 'bad' disk didn't turn out to have any bad sectors.)
>
> I was able to recover. The 0.99999980 copy of my damaged disk to the
> identical new one, using
>
> recoverdisk /dev/ad2 /dev/ad3
>
> turned out to have been successful. The program was still trying to
> improve the result but I didn't see any increase of recoverd block, so I
> terminated it.
>
> Just for the record: Before I wanted to give back in my faulty disk
> to my computer supplier as a case for warranty, I zeroed out the faulty
> disk.
>
> dd if=/dev/zero of=/dev/ad2 bs=1m
>
> It took half an hour to zero out the 80GB. Transferrate 44 MB/s?
> And not a single error ? Or is this normal?
>
> Then I tried to read back
>
> dd if=/dev/ad2 of=/dev/zero bs=2m
>
> Yes, just for the fun I said 2m blocksiye. And now we come back
> to FreeBSD contents:
>
> The system froze at this command (FreeBSD 5.2.1 on that machine)

I don't know if this is why the system froze, but /dev/zero is probably not a 
useful output device.  You could use of=/dev/null just to see if the disk 
reads succeed w/o errors.  I've also done "cmp /dev/adX /dev/zero" before, 
but you don't have any control over how the disk reads are handled that way.

JN