From: Bill Marcum on
["Followup-To:" header set to comp.os.linux.hardware.]
On 2010-03-07, Ant <ant(a)zimage.comANT> wrote:
> On 3/7/2010 12:47 AM PT, Yousuf Khan typed:
>
>> HOWTO enable core-dumps - LinuxReviews
>> http://en.linuxreviews.org/HOWTO_enable_core-dumps
>
> Thanks. Isn't this for program crashes, not kernel panics? I wonder why
> it was removed because I used to see those core files from crashes.

Core dumps are usually disabled by default because often they just take
up space and are never seen by anyone who knows how to interpret them.
Some software automatically mails a bug report to the developers if it
crashes.
From: Ant on
On 3/7/2010 3:26 PM PT, Bill Marcum typed:

>>> HOWTO enable core-dumps - LinuxReviews
>>> http://en.linuxreviews.org/HOWTO_enable_core-dumps
>>
>> Thanks. Isn't this for program crashes, not kernel panics? I wonder why
>> it was removed because I used to see those core files from crashes.
>
> Core dumps are usually disabled by default because often they just take
> up space and are never seen by anyone who knows how to interpret them.
> Some software automatically mails a bug report to the developers if it
> crashes.

Thanks. :)
--
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From: Yousuf Khan on
Arno wrote:
> You don't need to, no disk access is possible after a kernel
> panic, hence no loging. The only thing you can do, is to
> look at the screen or to enable the serial console output and
> log that on another machine.
>
> The reason no disk access is possible is simple: A kernel
> panic only hapens when the kernel internal state is regarded
> as seriously corrupted. A disk access could then cause serious
> filesystem corruption (at least writing) and is therefore
> not done.
>
> Arno

However, it doesn't look like his problems are actually disk related.
The disk-related messages just seem to coincidental and minor.

Yousuf Khan
From: Bob on
On 03/07/2010 02:54 PM, Rod Speed wrote:
> Yousuf Khan wrote
>> Pascal Hambourg wrote
>>> Rod Speed wrote
>>>> Pascal Hambourg wrote
>
>>>>> Aren't pending sectors sectors waiting to be remapped because of read errors ?
>
>>>> Thats not the same thing as unreadable sectors.
>
>>> Aren't pending sectors unreadable, because of read errors ?
>
>> Pending sectors are still readable,
>
> Some of them are unreadable, just not all of them are.
>
>> but they are weak when it comes time to write to them. So they are pending remapping during the next write to them.
>
> Even unreadable sectors are marked as pending until the write, so you
> can attempt to get what data is in them before the write/reallocate.
>

More importantly, it's so that you will continue to get an I/O error when
you try to read the file that contains that sector. It would be a Very
Bad Thing (tm) if you got whatever junk was in the reallocated sector
(remember, the drive could not recover the original data) with no error
indication.

Even if the bad sector is part of your file system's free space or is
otherwise irrelevant, the drive has no way to know that. The drive has
to keep the bad sector visible to the OS until you direct a write there,
at which point the original content is no longer relevant.

--
Bob Nichols AT comcast.net I am "RNichols42"
From: Rod Speed on
Bob wrote
> Rod Speed wrote
>> Yousuf Khan wrote
>>> Pascal Hambourg wrote
>>>> Rod Speed wrote
>>>>> Pascal Hambourg wrote

>>>>>> Aren't pending sectors sectors waiting to be remapped because of read errors ?

>>>>> Thats not the same thing as unreadable sectors.

>>>> Aren't pending sectors unreadable, because of read errors ?

>>> Pending sectors are still readable,

>> Some of them are unreadable, just not all of them are.

>>> but they are weak when it comes time to write to them. So they are pending remapping during the next write to them.

>> Even unreadable sectors are marked as pending until the write, so you
>> can attempt to get what data is in them before the write/reallocate.

> More importantly, it's so that you will continue to get an I/O error when you try to read the file that contains that
> sector.

That doesnt happen. If you get a good read, you wont get an I/O error.

> It would be a Very Bad Thing (tm) if you got whatever junk was in the reallocated sector

The normal read check stops that from happening, it
doesnt have to be flagged as a pending sector to get that.

> (remember, the drive could not recover the original data) with no error indication.

You will always get an error indication if it couldnt be read, and
dont need one if it could be read because the read success varys.

> Even if the bad sector is part of your file system's free space or is otherwise irrelevant, the drive has no way to
> know that.

Yes, but it doesnt need to know that because if its part of the
free space it will normally only be written to, not read from.

> The drive has to keep the bad sector visible to the OS until you direct a write there,

No it does not. It could reallocate the sector on enough bad
reads of that sector, and not bother about the data in that sector.

> at which point the original content is no longer relevant.