Changes between Version 15 and Version 16 of FAQ


Ignore:
Timestamp:
Sep 28, 2009, 2:30:05 AM (10 years ago)
Author:
Gabriele Pohl
Comment:

Integrate explanation about similiar errors on SCSI disks

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  • FAQ

    v15 v16  
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    319 === {{{smartd}}} is warning that my ATA disk has unreadable or uncorrectable or pending sectors. What's going on? ===
    320 
    321 Disk drives store data in blocks (sectors) of 512 bytes.  Each 512 bytes has additional bytes appended to it (usually 40 to 60) which are used internally by the disk firmware for error checking/detection and correction.  These are called ECC bytes.
     319=== ''Medium Error'' or ''unreadable or uncorrectable or pending sectors'' on disk. What's going on? ===
     320
     321SCSI and ATA disk drives store data in blocks (sectors) of 512 bytes. Each 512 bytes of user data is stored on the media plus 40 or more bytes of ECC data included in it. These - so called ''ECC Bytes'' - are used internally by the disk firmware for error checking/detection and correction.
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    323323Sometimes the data in a sector gets corrupted.  This can happen because a speck of dust scratched the disk, or because the disk was powered down while writing data to that sector, or for other reasons. Usually the ECC bytes can be used to correct the corrupted data. However if the ECC bytes are inconsistent or can't be used to correct the bad data, then the 512 bytes of data are lost.  Such a sector is called unreadable or uncorrectable.
     
    327327Disks with uncorrectable sectors can often be repaired by using the disk manufaturer's 'disk evaluation and repair' utility (see previous FAQ entry).  Beware: this may force reallocation of the lost sector and thus corrupt or destroy any file system on the disk. See [http://smartmontools.sourceforge.net/badblockhowto.html Bad block HOWTO] for generic Linux instructions.
    328328
    329 Normally when an uncorrectable sector is found, the disk puts this onto a 'pending sector list' to indicate that it should be replaced with a spare good sector.  However this replacement won't take place until either the disk can read the data on the bad sector, or is commanded to write new data to that bad sector.
     329Normally when an uncorrectable sector is found, the disk puts this onto a 'pending sector list' to indicate that it should be replaced with a spare good sector.  However this replacement won't take place until either the disk can read the data on the bad sector, or is instructed to write new data to that bad sector.
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