Re: Using CentOS 7 to attempt recovery of failed disk

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In article <CACXMG+s-KcfMV_eFRqm12asaQ8rDABL123bD+ur8jwNVLyQXjw@xxxxxxxxxxxxxx>,
Erick Perez - Quadrian Enterprises <eperez@xxxxxxxxxxxxxxx> wrote:
> @tonymountifield
> Does this still hold true?
> https://superuser.com/a/1075837

It wouldn't surprise me. What I take away from those tests is that it is indeed
important to use a bs= setting that corresponds to the disk physical block size,
which is why I said to use bs=4096.

When I used "conv=noerror,sync bs=4096" I got an image of the correct size.
That seems to correspond with what is said in the comment you linked to.

Cheers
Tony

> On Sun, Sep 27, 2020 at 7:21 AM Tony Mountifield <tony@xxxxxxxxxxxxx> wrote:
> 
> > In article <E02FA554-9D6D-4E7D-8A78-5FBDE1DE939D@xxxxxxxxxxxxxxxxx>,
> > Valeri Galtsev <galtsev@xxxxxxxxxxxxxxxxx> wrote:
> > >
> > >
> > > > On Sep 26, 2020, at 8:05 AM, Jerry Geis <jerry.geis@xxxxxxxxx> 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 â?¦
> > >
> > > 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: tony@xxxxxxxxxxxxx - http://www.softins.co.uk
> > Play: tony@xxxxxxxxxxxxxxx - http://tony.mountifield.org
> > _______________________________________________
> > CentOS mailing list
> > CentOS@xxxxxxxxxx
> > https://lists.centos.org/mailman/listinfo/centos
> >
> 
> 
> -- 
> 
> ---------------------
> Erick Perez
> Quadrian Enterprises S.A. - Panama, Republica de Panama
> Skype chat: eaperezh
> WhatsApp IM: +507-6675-5083
> ---------------------
> _______________________________________________
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> https://lists.centos.org/mailman/listinfo/centos
> 


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