[ale] dd & unexpected soft update inconsistency, HUH ?

[Courtney Thomas]

On Fri, 2005-04-15 at 08:49, Stephan Uphoff wrote:
> On Fri, 2005-04-15 at 09:25, Courtney Thomas wrote:
> > I've been using dd for years to mirror my server HD without problems.
> > 
> > The command used is:	dd if=< original HD > of=< mirror HD >
> 
> I don't think dd is a good idea on a life file system ....
> ...but you probably know this so let's ignore this for now.
> 

Stephen,

Thank you for your help  :-)

I'm not doing this on a live file system. I'm booting up with a CD and
doing this on unmounted filesystems.

> > However, yesterday, for the first time, when I do this, I get the error:
> > 
> > 	UNEXPECTED SOFT UPDATE INCONSISTENCY
> > 
> > This happens to mirror HD /usr only.
> > Mirror HD / and /var do not exhibit this problem.
> > 
> > If I fsck the mirror HD, all is OK except mirror HD /usr in which I get
> > a plethora of errors complaining about soft update inconsistencies.
> > 
> > If I attempt to examine mirror HD /usr with ls -l, I see there's also a
> > raft of BAD FILE DESCRIPTORs.
> > 
> > Further, the dd completion screen shows... an error coming from the
> > original HD, i.e. not the mirrored HD, drive. It only reports "[original
> > HD] input error". But when I fsck all partitions of that original HD,
> > all is reported as satisfactory.
> 
> Looks like you have a bad sector somewhere on the disk.

I agree it looks like it, maybe. But why doesn't fsck find this ?

> Is there something in the log file?

Which log file ?

> The /usr partition is probably only partially copied.

You are correct on this too.
> 
> You can try the following:
> 1) tar up /usr so that all used data blocks will be read.
>    This may indicate an unreadable file .. or you may be lucky and the
> bad sector is in unused space.

tar needs a mounted filesystem right ? [I don't use tar.]

> 2) Locate the defect sector (dd to /dev/null with offset,counts...)

> 3) Write zeroes to the defect sector to "repair" it and fsck..

I understand the writing zeroes to the bad sector using an offset, but
how do I exactly determine how many zeroes to write ?

Also, I assume you recall that fsck gives no error message now.
 
> 4) Restore the file that was not readable in 1)	           
> 
> I believe that there are disk repair tools in the ports tree but never
> had the need to try them.
> 
> > What's goin' on here and how can I remedy it. This is my gateway server
> > and I urgently need to resolve this.
> > 
> > Appreciatively,
> > 
> > Courtney
> > 
> > 
> > 
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> > 
> > 
> 
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