In article <e02fa554-9d6d-4e7d-8a78-5fbde1de9...@kicp.uchicago.edu>,
Valeri Galtsev <galt...@kicp.uchicago.edu> wrote:
> 
> 
> > On Sep 26, 2020, at 8:05 AM, Jerry Geis <jerry.g...@gmail.com> wrote:
> > 
> > I have a disk that is flagging errors, attempting to rescue the data.
> > 
> > I tried dd first - if gets about 117G of 320G disk and stops incrementing
> > the save image any more.
> 
> did you try
> 
> dd conv=noerror …
> 
> this flag makes dd not stop on input error. Whatever is irrecoverable is 
> irrecoverable, but this way you will get stuff
> beyond failure point.

You need conv=noerror,sync so that unreadable sectors get replaced by zeros 
instead of not being written out at all.
Without sync, the filesystem geometry on the destination image will be wrong 
after the first error.

You also need bs=4096 so that ONLY the bad sector(s) get zeroed, and not the 
surrounding ones. If you have, say,
bs=1M, then you will get a megabyte of zeros if any block within that megabyte 
is bad.

I'm speaking from recent experience!

Cheers
Tony

-- 
Tony Mountifield
Work: t...@softins.co.uk - http://www.softins.co.uk
Play: t...@mountifield.org - http://tony.mountifield.org
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