Linux-kernel mailing list archive 2000-15,: Re: EXT2 and BadBlock updating.....

# Re: EXT2 and BadBlock updating.....

Ed Carp (erc@pobox.com)
Fri, 14 Apr 2000 09:07:29 -0500

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Stephen C. Tweedie (sct@redhat.com) writes:

> Hi,
>
> On Thu, Apr 13, 2000 at 07:03:53PM -0500, Ed Carp wrote:
> >
> > > > Most modern disks do this for you *transparently* - the driver doesn't even
> > > > see the error, so this does't really apply. If the kernel sees an error, it's
> > > > a real error, as opposed to one that has been remapped.
> > >
> > > Not quite. If you get a read error, the drive will do the remapping
> > > for you such that future writes to the same sector will be mapped
> > > elsewhere on disk. However, that transparent remapping cannot, by
> > > itself, restore the contents of the lost sector. The kernel will
> > > still see the read error --- it's only future contents of the same
> > > logical sector which will be remapped.
> >
> > "Real", not "read". What you are saying is true only for reads - for writes, the write is transparently redirected.
>
> You were talking about "real errors" and "transparently remapped" as
> if they were mutually exclusive. They are not --- not quite. A true
> read error causes a transparent remapping at the same time. It's just
> that the remap doesn't take effect until the next write: the bad
> sector is still marked by the drive immediately.

Sorry if I didn't make that clear. I wasn't quite sure how the reads were
handled, thanks for the info.

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