[wplug] help interperting errors in messages log

[Mike Griffin]

And for the background:

cyclic redundancy check

<algorithm> (CRC or "cyclic redundancy code") A number derived from,  
and stored or transmitted with, a block of data in order to detect  
corruption. By recalculating the CRC and comparing it to the value  
originally transmitted, the receiver can detect some types of  
transmission errors.

A CRC is more complicated than a checksum. It is calculated using  
division either using shifts and exclusive ORs or table lookup (modulo  
256 or 65536).

The CRC is "redundant" in that it adds no information. A single  
corrupted bit in the data will result in a one bit change in the  
calculated CRC but multiple corrupted bits may cancel each other out.

CRCs treat blocks of input bits as coefficient-sets for polinomials.  
E.g., binary 10100000 implies the polynomial: 1*x^7 + 0*x^6 + 1*x^5 +  
0*x^4 + 0*x^3 + 0*x^2 + 0*x^1 + 0*x^0. This is the "message  
polynomial". A second polynomial, with constant coefficients, is called  
the "generator polynomial". This is divided into the message  
polynomial, giving a quotient and remainder. The coefficients of the  
remainder form the bits of the final CRC. So, an order-33 generator  
polynomial is necessary to generate a 32-bit CRC. The exact bit-set  
used for the generator polynomial will naturally affect the CRC that is  
computed.

Most CRC implementations seem to operate 8 bits at a time by building a  
table of 256 entries, representing all 256 possible 8-bit byte  
combinations, and determining the effect that each byte will have. CRCs  
are then computed using an input byte to select a 16- or 32-bit value  
from the table. This value is then used to update the CRC.

Ethernet packets have a 32-bit CRC. Many disk formats include a CRC at  
some level.

(1997-08-02)



Mike


On Tuesday, August 19, 2003, at 12:30  PM, Mike Griffin wrote:

> CRC errors indicate bad blocks on the HDD. If you're trying to use a  
> CDROM and get CRC errors, the CDROM cannot be mounted. It's considered  
> "bad media"  I might be wrong with this, but unless a block is marked  
> "bad" the OS still tries to read from, and write to, these blocks  
> creating the error when the attempt is unsuccessful.
>
>
> Mike
>
>
> On Tuesday, August 19, 2003, at 11:30  AM, John Harrold wrote:
>
>> Sometime in August Vanco, Donald assaulted the keyboard and produced:
>>
>> | squeegy-wplug at squeegy.org wrote:
>> | > I have been getting errors daily like the below:
>> | >
>> | > 3 Time(s): end_request: I/O error, dev 03:02 (hda), sector 1017689
>> | > 14 Time(s): hda: read_intr: error=0x01 { AddrMarkNotFound },
>> | > LBAsect=1226534, sector=1017689
>> | > 2 Time(s): hda: read_intr: error=0x40 { UncorrectableError },
>> | > LBAsect=1226534, sector=1017689
>> | > 16 Time(s): hda: read_intr: status=0x59 { DriveReady SeekComplete
>> | > DataRequest Error }
>> | > 3 Time(s): ide0: reset: success
>> | 	
>> | 	It means your hard drive is very likely dying.  While there are
>> | steps that can be taken from a filesystem and manufacturer bad  
>> block level,
>> | but the fact is that the physical media on the drive is likely  
>> breaking
>> | down.  You can put off the inevitable for a while, but your disk is  
>> dying.
>> |
>> | 	If hda is simply a CD - it's bad media.
>> |
>>
>> on a similar note. i've had this error for a couple years on a  
>> workstation
>> in our lab. since all the important data is nfs mounted i didn't  
>> really
>> care so much if the drive died.
>>
>> Aug 18 kernel: had: dma_intr: status=0x51 { DriveReady SeekComplete  
>> Error }
>> Aug 18 kernel: had: dma_intr: error=0x84  { DriveStatusError BadCRC }
>>
>> can anyone shed some light on what this might be?
>>
>>
>> --  
>> ---------------------------------------------------------------------- 
>> ----
>>                                                | /"\
>>  john harrold                                  | \ / ASCII ribbon  
>> campaign
>>       jmh at member.fsf.org                    |  X  against HTML mail
>>            the most useful idiot               | / \
>> ---------------------------------------------------------------------- 
>> ----
>>  What difference does it make to the dead, the orphans, and the  
>> homeless,
>>  whether the mad destruction is brought under the name of  
>> totalitarianism or
>>  the holy name of liberty and democracy?
>>  --Gandhi
>> ---------------------------------------------------------------------- 
>> ----
>> gpg --keyserver keys.indymedia.org --recv-key F65A739E
>> ---------------------------------------------------------------------- 
>> ----
>> <mime-attachment>
>
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