[nSLUG] Multiply-claimed blocks?

Dop Ganger nslug at fop.ns.ca
Wed Aug 31 14:12:54 ADT 2011


On Wed, 31 Aug 2011, Mike Spencer wrote:
>
> Ben Armstrong <synrg at sanctuary.nslug.ns.ca> wrote:
>
>> However, cosmic rays are well known to cause bit flipping in RAM,...
>
> I'd heard that, of course. In this case, the corruption seems to have
> been in a lib file on HD that (AFAIK) is written at install time and never
> re-written unless upgrading or the like.  I had not heard that cosmic
> rays (energetic neutrons according to the article you cited) could flip
> a bit on a HD.  But, as you say, "Anything is possible...."

No reason a magnetic bit on a hard drive can't be flipped as well as a bit 
in a RAM chip. Drives also do a pretty good job of dying on their own - 
http://www.usenix.org/events/fast08/tech/full_papers/bairavasundaram/bairavasundaram_html/index.html 
is a slightly depressing paper on failure rates of hard drives in a large 
scale environment. I also vaguely recall hearing about a prof who ran a 
daily md5 of all the files in his ~, and regularly found checksum errors.

>> Keep a live system around for just such an occasion, e.g.
>>
>> http://www.debian.org/CD/live
>
> That Debian disk sounds like a good thing.  The fly in the ointment
> would be that the packages it holds for re-installing corrupted bits
> would be configured for Debian.  I have no idea what problems, if any,
> I might encounter in that account.  I wonder if someone has made a
> similar CD/DVD for Slack.  I shall have to look around.

Boot the Debian rescue disk (or any that take your fancy - I find Recovery 
Is Possible has a nice choice of tools), fix the disk, mount it on /mnt, 
then chroot /mnt and you are back in your Slackware environment to finish 
repairs. Exit out if you need to get back to the host environment (or 
switch tty).

Cheers... Dop.



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