RE: crypto and fsck guys

David Olofson (audiality@swipnet.se)
Tue, 19 Oct 1999 02:34:42 +0200


On Mon, 18 Oct 1999, Anonymous wrote:
> P.S. Thank you to Alan Cox for the backup comment - I
> know that it is easy to backup the data to tape. I do backup
> most stuff in case of HW failure, but don't expect the
> software to be at fault (no I don't think it was
> caused by random alpha particles hitting the disk -
> I've run several surface scans which reveal that the
> disk is fine).

I don't think you should trust hard drives that much. They are
complex and sensitive devices...

* They can crash the heads into the disk due to spindle
bearing failure or some problem with the heads or
seek motor.

* The electronics can fail, resulting in the data being
destroyed. (Happened to me *twice*!)

* A firmware bug can make the drive slam the heads into
the spindle, resulting in the heads crashing and
damaging the disk. (Also happened to me once...)

* The interface can fail, resulting in data being
destroyed.

* You can have a power surge, or a power supply failure
that fries most of your system, HDs included.

* Fire can destroy most things. Applies to data as well,
if it's not backed up.

As for surface scans; I don't know all that much about low level
progamming of modern HDs, so I might be missing something, but;

1) Unless the drive has some way of reporting the error
correction status (i e how many errors it has to
correct), the drive passing a surface scan only means
it's still ok; not that the data has the same quality
as when you wrote it.

2) AFAIK, the read cirquitry of most drives doesn't give
you more info than the data it can retrieve. (As in;
floppy drives report only digital data; you can't see
the actual analog signal from the disk w/o special
hardware, so you can't tell how close you are to
failure.)

I'm sorry about your data loss; I guess we all know what that feels
like, even if it's just a few hours of work that's lost...

Certainly, making the tools that handle important data as reliable
and safe as possible is good. However, after my 15 years of using
computers, I don't really trust *anything*. Any hardware or software
can fail, get stolen, be used incorrectly, or whatever... Expect it
to happen - that hurts less in the long run.

//David

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