Re: smartd
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.
Reply to: