Lots of mapped out bad sectors cause trouble?

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AIUI ... a bad sector on an IDE hard drive gets labelled as unusable
in the drive's map and a substitute sector is found. The user
wouldn't know about it because this happens transparently.

If there are LOTS of bad sectors then couldn't we have a situation
where the drive's performance is poor but there is no indication in
running drive diagnostics that there's anything wrong?

I have some hard drives which are much slower than similar ones.
Could a very large number of mapped out bad sectors be a *likely*
explanation for this?

BACKGROUND:  The difference is most easily observable when I do an
online defrag of NTFS's own files (such as $MFT).  The defragger
checks for and locks all data files before performing its defrag.  
The speed it does this varies enormously between drives.

The difference seems to be of another order of magnitude in size to
the differences which might be due to model, firmware level, type of
data, file system, etc.

Re: Lots of mapped out bad sectors cause trouble?

jack smith wrote:

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That last isnt necessarily true. If its bad on a read, it
wont get transparently remapped until its written to.

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No, essentially because remapping doesnt necessarily affect performance.

In practice the drive turns the LBA into CHS values mathematically
and the remapped sectors are just part of that maths, and so that
has no effect on performance.

And if a drive does have a large number of bads, its dying, and
will be retrying on the not completely bad sectors, so that will
have a much bigger effect on preformance, particularly the retrys.

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Very unlikely. Most likely they are just retrying on the not completely bads.

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That can be due to other effects. Some defraggers vary very
significantly speed wise just on the file detail, not the physical drive.

It can also just be that what look to you like similar drives are very
different physically, particularly sectors per track and seek times.

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Post the Everest SMART stats on the best and worst drives.
That will at least show what bad sectors the drives have.

Re: Lots of mapped out bad sectors cause trouble?

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You can get poor performance, however not really from the remapping.
You get it while the drive is trying to recover the sectors it is
eventually going to remap.

But you can get this diagnised, just look at the SMART attribute
for remapped sector count raw value.

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Not really.

Drives at most remap a few 1000 sectors. That is not enough for a
strong performance degradation. Drives that remap this many
sectors are also typically in the process of dying.

You likely have a different issue, or it may just be natural speed


Re: Lots of mapped out bad sectors cause trouble?

finger to keyboard and composed:

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If a drive experiences more than 6 CRC errors, Windows XP degrades its
performance from DMA mode to PIO.

See http://winhlp.com/node/10

To check for bad sectors, try a SMART utility such as HD Sentinel
(Linux & Windows):
http://www.hdsentinel.com /

For benchmarking, try HD Tune:
http://www.hdtune.com /

Here are more SMART diagnostic tools:


smartmontools (Linux/Windows):
http://sourceforge.net/projects/smartmontools/files /

See this article for SMART info:
http://en.wikipedia.org/wiki/S.M.A.R.T .

Comparison of S.M.A.R.T. tools:

- Franc Zabkar
Please remove one 'i' from my address when replying by email.

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