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Re: smartd

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On Sunday, January 23, 2022 10:57:53 AM tomas@tuxteam.de wrote:
> On Sun, Jan 23, 2022 at 08:14:06AM -0700, Charles Curley wrote:
> > On Sun, 23 Jan 2022 11:09:47 +0000
> > 
> > Andy Smith <andy@strugglers.net> wrote:
> > > Yes. When a drive sector goes bad, the drive cannot read from it, so
> > > you get an error in Linux when a read is attempted.
> > 
> > As I understand things, that isn't entirely correct. From what I
> > understand:
> > 
> > If the drive can read a sector without error, it passes the data to the
> > OS and that's it.
> > 
> > If it gets an error, it uses cyclical redundancy check (CRC) data to
> > reconstruct the data. If that fails, it reports an error to the OS. If
> > the CRC reconstruction is successful, the drive re-writes the sector
> > and passes the reconstructed data back to the OS.
> 
> It is actually more complicated as this. As I understand this Wikipedia
> entry [1], some errors while reading a block are to be expected: it
> seems to be more profitable to push the density to the limit where error
> correction picks up some rest. Only when the error rate surpasses some
> threshold the block is remapped.
> 
> I guess SMART counts the latter events, but actually I have no idea :)
> 
> And the error correction codes are a bit more sophisticated than plain
> CRC: Reed-Solomon or, more modern, low-density parity-check codes.

I would guess that the actual details vary depending  on the manufacturer and 
the revision level of the manufacturers firmware on the drive.

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smartd peter@easthope.ca - 2022-01-22 19:30 +0100
  Re: smartd Dan Ritter <dsr@randomstring.org> - 2022-01-22 20:00 +0100
    Re: smartd peter@easthope.ca - 2022-01-23 16:50 +0100
    [SOLVED] Re: smartd peter@easthope.ca - 2022-02-04 18:20 +0100
  Re: smartd Andy Smith <andy@strugglers.net> - 2022-01-22 20:10 +0100
    Re: smartd peter@easthope.ca - 2022-01-23 07:00 +0100
      Re: smartd Andy Smith <andy@strugglers.net> - 2022-01-23 12:20 +0100
        Re: smartd Charles Curley <charlescurley@charlescurley.com> - 2022-01-23 16:20 +0100
          Re: smartd <tomas@tuxteam.de> - 2022-01-23 17:00 +0100
            Re: smartd rhkramer@gmail.com - 2022-01-24 18:20 +0100
    Re: smartd peter@easthope.ca - 2022-01-23 18:10 +0100
      Re: smartd Linux-Fan <Ma_Sys.ma@web.de> - 2022-01-23 19:20 +0100
        Re: smartd Andy Smith <andy@strugglers.net> - 2022-01-23 19:50 +0100
          Re: smartd Charles Curley <charlescurley@charlescurley.com> - 2022-01-23 22:20 +0100
        Re: smartd Andrei POPESCU <andreimpopescu@gmail.com> - 2022-01-25 10:50 +0100
    [SOLVED] Re: smartd peter@easthope.ca - 2022-02-04 19:10 +0100
  Re: smartd Charles Curley <charlescurley@charlescurley.com> - 2022-01-22 22:50 +0100

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