Re: [smartmontools-support] Which attributes can estimate number of bad blocks?

[Tim S. <ti...@se...>]

On 01/08/16 20:48, ro...@sp... wrote:
> All I can tell you is while 1 or 2 bad sectors (hard errors, not medium)
> don't mean it's a bad drive, every time a sector gets reallocated, the
> [platter] drive gets more fragmented. You can't defrag this. That's one of
> the reasons why when I hear complaints about a slow system or hard drive,
> the first thing I check is the SMART attributes. I'd say in at least 50%
> of the cases, it is indeed the hard drive going bad.

Given that the reallocated sectors are such a minuscule percentage of
the total number of sectors on a modern drive, I think that even with
>1000 sectors reallocated, the impact of fragmentation is likely to be
very slight.

On the other hand, a high number of reallocated sectors frequently goes
hand-in-hand with numerous read-retries (these are normally successful,
but time consuming if they are the 'offline' type), and this is more
likely to significantly hit performance.

In other words, the poor performance and the reallocated sectors may
both be symptoms of widespread (and potentially deteriorating) problems
on the drive, but I don't think the former is likely to be a direct
result of the latter...

Personally, I run monthly long self tests with smartd (these can both
catch bad sectors that you otherwise wouldn't have known about, and also
effectively "scrub" weak sectors, so are definitely worth doing), and
pro-actively replace drives which have rapidly or just steadily
increasing reallocated sector counts.

Although it's relatively rare, I've had drives which have been happily
operating for years with a reallocated sector count of a few tens,
without any further problems.  I've put these down to a one-off event or
very localised manufacturing defect within the drive.

HTH,

Tim.

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