kernel panic(?) trying to copy data off failed drive with dd

[Oliver Fromme]

Michael P. Soulier <msoulier at digitaltorque.ca> wrote:
 > Oliver Fromme said:
 > > So, if your panic is caused purely by software error, and
 > > it's not already known and documented, filing a PR might be
 > > a good idea.  But if faulty hardware is involved, sending
 > > a PR is probably useless.
 > 
 > I would think that it would depend on how the hardware is being used.

Yes, I agree.

 > If the
 > disk with errors happens to hold the swap partition, then it's difficult to
 > blame the kernel for crashing. If it's simply reading data, I don't think that
 > a kernel panic is acceptable.

"Simply reading data" would be a software error, and in
that case a crash or freeze is not acceptable.  (Although
it may be very difficult to fix, especially without
sacrificing performance significantly, e.g. see mount(8).)

However, if the _hardware_ is broken, i.e. the disk drive
does not respond correctly, for example producing DMA errors,
locking up the bus, or whatever, anything could happen.
I guess Søren could tell interesting stories about such
cases.  :-)

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd
Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.

"... there are two ways of constructing a software design:  One way
is to make it so simple that there are _obviously_ no deficiencies and
the other way is to make it so complicated that there are no _obvious_
deficiencies."        -- C.A.R. Hoare, ACM Turing Award Lecture, 1980