Re: chkdsk /r and surface scan

Well said. The first sign of trouble is always the best time to replace a
hard drive. The price of new one is less than the price for the time and
aggravation of replacing it after it's failed.

Kerry

"cquirke (MVP Windows shell/user)" <cquirkenews@xxxxxxxxxxxxxxx> wrote in
message news:8q6cb1hepfmmqv6ddngs6aek5gts5s8p57@xxxxxxxxxx
>
> Not really, no.
>
> If your HD's dying, do you want to know that early, when the first bad
> sector comes to light, or when it dies and eats your data?
>
> The fact that the drive "worked a lot better afterwards" suggests that
> the process did indeed "fix" bad sectors. That there were bad sectors
> to be found, is reason to immediately evacuate your data and get off
> that HD. If ChkDsk "fixed" (i.e. covered up) bad sectors and did not
> tell you it did so, then that's reason enough to not trust ChkDsk.
>
> Think about it - if you ever see a disk error, it means:
> 1) The HD's firmware defect management couldn't cover it up
> 2) The NTFS drivers couldn't cover it up
>
> Both (1) and (2) work in the same way, but at different levels of
> awareness. (1) works within the HD itself, and is invisible to the
> OS; your only window into the process is S.M.A.R.T. records, that only
> a detailled S.M.A.R.T. reporter will show you (many HD vendor's tools
> will just show you a glib "S.M.A.R.T. says the HD's OK").
>
> In contrast, (2) is - or should be - visible to the OS; you'd expect
> bad clusters to be marked out of use within the file system, and you'd
> hope that ChkDsk (or AutoChk) would log the details of this; not just
> new ones, but count of existing ones. However, you may find there's
> no way to get the OS to show you this info.
>
> Now it may be impossible to switch off the HD's own firmware defect
> management. If so, then whenever NTFS's driver code, or a surface
> scan via ChkDsk /r, "sticks" on a failing sector, the firmware itself
> is probably trying to hide it. Chances are these two competing
> processes will tangle up, causing a long delay that looks like a hang.
>
> Think about it; let's say NTFS tries to read the sector 100 times, and
> the firmware tries 100 times, too. Each time NTFS tries, this causes
> the firmware to try 100 times, making it 10 000 times in all, but
> here's the thing; a successful read is 100 times more likely to happen
> while the firmware's retrying, than when the NTFS is retrying, unless
> the sector is so dead that all the retries in the world can't help.
>
> Both processes try to do the same thing; read the data out of the
> dying sector, verify the data's OK via an integrity check (CRC or
> something), and if it's OK, write this data somewhere else that
> doesn't suck. But a bit pun might pass CRC with bad data, and what
> happens if the data can't be read at all? Just copy nothing to the
> new place, swap the pointers, and hope no-one notices?
>
> If the firmware does the remapping, the OS is unaware of it, unless it
> gets suspicious about the number of retries or has some sort of
> real-time awareness. If it does, it may remap the data itself anyway,
> but when the OS does it, it has to amend the volume's file system
> structure, and somehow mask the bad sector from re-use.
>
> What this means is you could have a really sick HD that looks "OK" to
> ChkDsk or Scandisk, because all defects are hidden by the firmware.
> There may be a substantial number of bad sectors remapped at the HD's
> firmware level, and not a single adverse finding by ChkDsk or
> Scandisk, but because better sectors are used, the HD speeds up.
>
> To me, that's a clear call to head for the lifeboats.
>
> You may want to know what I say that, if these bad sectors are
> "fixed". Well, that's because while every HD may have initial
> manufacturing defects that are mapped out, *new* defects are
> significant. Why would there be new defects? Surface wear? If so,
> the internal airspace is probably polluted with abrasive debris; where
> the heads go, further wear is likely to follow. Or is it something
> awry with the head quality or positioning? Same mileage; if it's gone
> from fine to bad, it will progress from bad to worse.
>
> You need to know that, but everything conspires to hide that from you,
> so you can stagger on until the HD goes out of warranty.
>
>
>
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