increasing dd disk to disk transfer rate

[Christoph P. Kukulies]

Thanks, folks, for the interesting contributions. I really should
have marked the subject "OT" but there spring up a lot
of interesting ideas.

On Fri, Jan 13, 2006 at 08:13:00AM +1100, Peter Jeremy wrote:
> On Thu, 2006-Jan-12 10:48:38 +0100, Christoph Kukulies wrote:
> >dd if=/dev/ad2 of=/dev/ad3 conv=noerror
> >
> >The process is running now since yesterday evening and it is at 53 MB
> >at a transfer rate of about 1.1 MB/s.
> >
> >In case the the result being unusable I would like to find a way to make this
> >copying faster.
> 
> Note that whilst increasing the DD blocksize will speed up the
> transfer, it will also increase the amount of collateral damage when a
> hard error occurs.  If you rummage around the ports or tools tree,
> you'll find a utility (its name escapes me but I believe it was
> written by phk) that is designed to do disk-to-disk recovery - it


/usr/src/tools/tools/recoverdisk  

I fired up this tool yesterday night and it is still running. Ah yes, it
runs forever unless it empties the queued failed block reads.
It writes out a line of numbers (which are a bit difficult to understand).

I think the suggestion to do a filewise recovery would be the best since
it will be very unlikely



> copys data in big slabs until it gets an error and then works around
> the faulty area block by block.
> 
> You should also install /usr/ports/sysutils/smartmontools - this
> handles S.M.A.R.T.

Yes, but what would smart help me further with recovery?
> 
> >Is there a way to tweak the driver (be it the FreeBSD promise driver
> >or the normal ata driver) to use more retries on errors so that I
> >have the chance to copy everything or nearly everything of the already
> >degrading hard disk?
> 
> A quick look at the ata driver suggests that there are a number of
> 'retry' and 'retries' variables/fields.  I suspect you could increase
> the number of retries if you wanted to patch the driver.


Thanks for the help.


--
Chris Christoph P. U. Kukulies kuku_at_kukulies.org