"andy" wrote in message
...
Hi!
Could someone please explain why in the case of *mechanical* failure HD
becomes sometimes undetected by BIOS and/or the operating system (e.g. win
xp
or linux)?

*Sometimes* ... So, maybe it's the nature of the problem that prevents the
disk from being detected.

If it was an electronic failure then such behaviour would be obious, but
why
the same happens with some mechanical failures? When electronics is
working in
my opinion

It is hardly a matter of opinion ...

it still should be detected by bios and/or the system (win xp or
linux), but often it is not.
I could recover about 80% of the data from my HDD

How do you know? How did you come up with the 80%?

(which apparently has a
mechanical failure - plates spin up and down, heads create bad noises) if
only
the disk could be seen by the system all the time. But often during
copying of
the data heads hit with a loud sound so badly that sometimes even the
plates
stop rotating, and the disk then dissapears from the system. It is then
very
difficult to make it detectable by the system again, sometimes the sytem
can
detect it but only after several minutes of copying it freezes and then
dissapears again.

You should try to clone it as long as you can see it. However, every read
may worsen the condition of the disk, in general it is advised to cease DIY
recovery attempts (if the data is important to you) when a disk is maing
unusual and scary noises.

Recently, I was unlucky, and even after several dozens of retries it's
still
undetectable by the system.

Could you please advice what to do to make the disk detectable by the
system
all the time?

Your issue is a psychological one. You can not accept that there are
situations you can not resolve and have no control over. Apart from
contacting a data recovery lab, you also need to work out this problem.

BTW, if someone has the same disk model (Quantum Fireball ST64A011),
please
let me know.


Why do you want to know?

--
Joep