Re: About USB hard drives and errors
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Tony Nelson wrote:
> If the data in a sector was not readable, the sector
> will be listed as "Pending". Pending sectors are much worse than
> Reallocated sectors, as Pending sectors mean lost data (if the sector
> was in actual use, which SMART does not know -- and figuring out which
> file might have been affected is, umm, tedious).
OK. Usually (during regular use) the internal errors probably increase
more slowly. If a single sector is already really unreadable, then every
last one of the internal error correction mechanisms has already tried
and failed. Such many errors probably indicate that either the HD is
terminally worn out, or that a sector got damaged due to external
influences. Either way, I would not use such a HD any more.
> I keep SMART's Offline Surface Scan enabled on my drives, to have the
> best chance that any failing sectors will be noticed early while they
> can still be recovered. I don't mind if there are a few Reallocated
> sectors, as long as there are never any Pending sectors. I'd mind if
> the number of Reallocated sectors kept increasing. Of course, I also
> keep backups.
Good practice. But I believe that HDs always try to recover failing
sectors whenever possible, with or without offline surface scan.
Presumably sectors are remapped when the number of errors is still way
below the maximum of correctable errors.
The world outside the HD never hears anything about it unless they ask
the HD to report the SMART tables.
>> In other words, scanning for bad blocks on a HD cannot work.
>
> Or at least normally won't, unless Data Has Been Lost.
Yes, that's what I meant. It does work for proving for sure that the HD
is broken. And to push a HD over the edge which is about to break
(useful particularly for people with backups). I was assuming that the
HD does not contain data, since the write test of badblocks deletes
everything anyway and does not restore the original.
Speaking of, does anybody know why the programmers of badblocks left out
the ability to write the original content back after a read-write scan?
That makes no sense to me.
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