[ZT]如何修复linux硬盘坏块（bad block howto）

http://smartmontools.sourceforge.net/BadBlockHowTo.txt

(先贴这里，有空会翻译下)

THIS DOCUMENT SHOWS HOW TO IDENTIFY THE FILE ASSOCIATED WITH AN
UNREADABLE DISK SECTOR, AND HOW TO FORCE THAT SECTOR TO REALLOCATE.

 

Assumptions: Linux OS, ext2 or ext3 file system.

Bruce Allen

Thanks to Sergey Vlasov, Theodore Ts'o, Michael Bendzick, and others
for explaining this to me. I would like to add text showing how to do
this for other file systems, in particular ReiserFS, XFS, and JFS:
please email me if you can provide this information.

 

NOTE: Starting with GNU coreutils release 5.3.0, dd on Linux includes
options 'iflag=direct' and 'oflag=direct'.  Using these with the dd commands
below should be helpful, because adding these flags should avoid any interaction
with the block buffering IO layer in Linux and permit direct reads/writes
from the raw device.  Use 'dd --help' to see if your version of dd supports
these options. If not, build the latest code from
fttp://alpha.gnu.org/gnu/coreutils.

 

In this example, the disk is failing self-tests at Logical Block
Address LBA = 0x016561e9 = 23421417.  The LBA counts sectors in units
of 512 bytes, and starts at zero.

 

-----------------------------------------------------------------------------------------------
root]# smartctl -l selftest /dev/hda:

 

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed: read failure       90%       217         0x016561e9
-----------------------------------------------------------------------------------------------

 

Note that other signs that there is a bad sector on the disk can be
found in the non-zero value of the Current Pending Sector count:
-----------------------------------------------------------------------------------------------
root]# smartctl -A /dev/hda
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       1
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       1
-----------------------------------------------------------------------------------------------

 

First Step: We need to locate the partition on which this sector of
the disk lives:
-----------------------------------------------------------------------------------------------
root]# fdisk -lu /dev/hda

 

Disk /dev/hda: 123.5 GB, 123522416640 bytes
255 heads, 63 sectors/track, 15017 cylinders, total 241254720 sectors
Units = sectors of 1 * 512 = 512 bytes

 

   Device Boot    Start       End    Blocks   Id  System
/dev/hda1   *        63   4209029   2104483+  83  Linux
/dev/hda2       4209030   5269319    530145   82  Linux swap
/dev/hda3       5269320 238227884 116479282+  83  Linux
/dev/hda4     238227885 241248104   1510110   83  Linux
-----------------------------------------------------------------------------------------------

 

The partition /dev/hda3 starts at LBA 5269320 and extends past the
'problem' LBA.  The 'problem' LBA is offset 23421417 - 5269320 =
18152097 sectors into the partition /dev/hda3.

 

To verify the type of the file system and the mount point, look in
/etc/fstab:
-----------------------------------------------------------------------------------------------
root]# grep hda3 /etc/fstab
/dev/hda3 /data ext2 defaults 1 2
-----------------------------------------------------------------------------------------------
You can see that this is an ext2 file system, mounted at /data.

 

Second Step: we need to find the blocksize of the file system
(normally 4096 bytes for ext2):
-----------------------------------------------------------------------------------------------
root]# tune2fs -l /dev/hda3 | grep Block
Block count:              29119820
Block size:               4096
-----------------------------------------------------------------------------------------------
In this case the block size is 4096 bytes.

 

Third Step: we need to determine which File System Block contains this
LBA.  The formula is:
  b = (int)((L-S)*512/B)
where:
b = File System block number
B = File system block size in bytes
L = LBA of bad sector
S = Starting sector of partition as shown by fdisk -lu
and (int) denotes the integer part.

 

In our example, L=23421417, S=5269320, and B=4096.  Hence the
'problem' LBA is in block number
   b = (int)18152097*512/4096 = (int)2269012.125
so b=2269012.

 

Note: the fractional part of 0.125 indicates that this problem LBA is
actually the second of the eight sectors that make up this file system
block.

 

Fourth Step: we use debugfs to locate the inode stored in this block,
and the file that contains that inode:
-----------------------------------------------------------------------------------------------
root]# debugfs
debugfs 1.32 (09-Nov-2002)
debugfs:  open /dev/hda3
debugfs:  icheck 2269012
Block Inode number
2269012 41032
debugfs:  ncheck 41032
Inode Pathname
41032 /S1/R/H/714197568-714203359/H-R-714202192-16.gwf
-----------------------------------------------------------------------------------------------

 

In this example, you can see that the problematic file (with the mount
point included in the path) is:
/data/S1/R/H/714197568-714203359/H-R-714202192-16.gwf

 

To force the disk to reallocate this bad block we'll write zeros to
the bad block, and sync the disk:
-----------------------------------------------------------------------------------------------
root]# dd if=/dev/zero of=/dev/hda3 bs=4096 count=1 seek=2269012
root]# sync
-----------------------------------------------------------------------------------------------

NOTE: THIS LAST STEP HAS PERMANENTLY AND IRRETREVIABLY DESTROYED SOME
OF THE DATA THAT WAS IN THIS FILE.  DON'T DO THIS UNLESS YOU DON'T
NEED THE FILE OR YOU CAN REPLACE IT WITH A FRESH OR CORRECT VERSION.

Now everything is back to normal: the sector has been reallocated.
Compare the output just below to similar output near the top of this
article:
-----------------------------------------------------------------------------------------------
root]# smartctl -A /dev/hda
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       1
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       1
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       1
-----------------------------------------------------------------------------------------------

 

Note: for some disks it may be necessary to update the SMART Attribute values by using
smartctl -t offline /dev/hda

 

The disk now passes its self-tests again:

-----------------------------------------------------------------------------------------------
root]# smartctl -t long /dev/hda  [wait until test completes, then]
root]# smartctl -l selftest /dev/hda

 

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%       239         -
# 2  Extended offline    Completed: read failure       90%       217         0x016561e9
# 3  Extended offline    Completed: read failure       90%       212         0x016561e9
# 4  Extended offline    Completed: read failure       90%       181         0x016561e9
# 5  Extended offline    Completed without error       00%        14         -
# 6  Extended offline    Completed without error       00%         4         -
-----------------------------------------------------------------------------------------------

 

and no longer shows any offline uncorrectable sectors:

-----------------------------------------------------------------------------------------------
root]# smartctl -A /dev/hda
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       1
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       1
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0
-----------------------------------------------------------------------------------------------

 

 

A SECOND EXAMPLE

On this drive, the first sign of trouble was this email from smartd:

    To: ballen
    Subject: SMART error (selftest) detected on host: medusa-slave166.medusa.phys.uwm.edu

 

    This email was generated by the smartd daemon running on host:
    medusa-slave166.medusa.phys.uwm.edu in the domain: master001-nis

 

    The following warning/error was logged by the smartd daemon:
    Device: /dev/hda, Self-Test Log error count increased from 0 to 1

 

   
Running smartctl -a /dev/hda confirmed the problem:
   
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed: read failure       80%       682         0x021d9f44

 

Note that the failing LBA reported is 0x021d9f44 (base 16) = 35495748 (base 10)
   
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       3
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       3

 

and one can see above that there are 3 sectors on the list of pending
sectors that the disk can't read but would like to reallocate.

 

The device also shows errors in the SMART error log:

Error 212 occurred at disk power-on lifetime: 690 hours
  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  40 51 12 46 9f 1d e2  Error: UNC 18 sectors at LBA = 0x021d9f46 = 35495750

 

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC   Timestamp  Command/Feature_Name
  -- -- -- -- -- -- -- --   ---------  --------------------
  25 00 12 46 9f 1d e0 00 2485545.000  READ DMA EXT

 

Signs of trouble at this LBA may also be found in SYSLOG:

[root]# grep LBA /var/log/messages | awk '{print $12}' | sort | uniq
 LBAsect=35495748
 LBAsect=35495750

 

So I decide to do a quick check to see how many bad sectors there
really are. Using the bash shell I check 70 sectors around the trouble
area:
   
[root]# export i=35495730
[root]# while [ $i -lt 35495800 ]
        > do echo $i
        > dd if=/dev/hda of=/dev/null bs=512 count=1 skip=$i
        > let i+=1
        > done
 
  

 

35495734
1+0 records in
1+0 records out
35495735
dd: reading `/dev/hda': Input/output error
0+0 records in
0+0 records out

 

35495751
dd: reading `/dev/hda': Input/output error
0+0 records in
0+0 records out
35495752
1+0 records in
1+0 records out

 

which shows that the seventeen sectors 35495735-35495751 (inclusive)
are not readable.

 

Next, we identify the files at those locations.  The partitioning
information on this disk is identical to the first example above, and
as in that case the problem sectors are on the third partition
/dev/hda3.  So we have:
     L=35495735 to 35495751
     S=5269320
     B=4096
so that b=3778301 to 3778303 are the three bad blocks in the file
system.

 

[root]# debugfs
debugfs 1.32 (09-Nov-2002)
debugfs:  open /dev/hda3
debugfs:  icheck 3778301
Block   Inode number
3778301 45192
debugfs:  icheck 3778302
Block   Inode number
3778302 45192
debugfs:  icheck 3778303
Block   Inode number
3778303 45192
debugfs:  ncheck 45192
Inode   Pathname
45192   /S1/R/H/714979488-714985279/H-R-714979984-16.gwf
debugfs:  quit

 

And finally, just to confirm that this is really the damaged file:

[root]# md5sum /data/S1/R/H/714979488-714985279/H-R-714979984-16.gwf
md5sum: /data/S1/R/H/714979488-714985279/H-R-714979984-16.gwf: Input/output error

 

Finally we force the disk to reallocate the three bad blocks:
[root]# dd if=/dev/zero of=/dev/hda3 bs=4096 count=3 seek=3778301
[root]# sync

 

We could also probably use:
[root]# dd if=/dev/zero of=/dev/hda bs=512 count=17 seek=35495735

 

At this point we now have:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0

 

which is encouraging, since the pending sectors count is now zero.
Note that the drive reallocation count has not yet increased: the
drive may now have confidence in these sectors and have decided not to
reallocate them..

 

A device self test:
  [root#] smartctl -t long /dev/hda
(then wait about an hour) shows no unreadable sectors or errors:

 

Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%       692         -
# 2  Extended offline    Completed: read failure       80%       682         0x021d9f44

 

[USEFUL HINTS ADDED BY OTHERS]

---------------------------------------------------------------------------

From: Kay Diederichs
                                                                                                                             
I read your badblocks-howto at
http://smartmontools.sourceforge.net/BadBlockHowTo.txt and greatly
benefitted from it. One thing that's (maybe) missing is that often the
"smartctl -t long" scan finds a bad sector which is _not_ assigned to
any file. In that case it does not help to run debugfs, or rather
debugfs reports the fact that no file owns that sector. Furthermore,
it is somewhat laborious to come up with the correct numbers for
debugfs, and debugfs is slow ...
                                                                                                                             
So what I suggest in the case of presence of
Current_Pending_Sector/Offline_Uncorrectable errors is to create a
huge file on that filesystem.
  dd if=/dev/zero of=/some/mount/point bs=4k
creates the file. Leave it running until the partition/filesystem is
full. This will make the disk reallocate those sectors which do not
belong to a file. Check the "smartctl -a" output after that and make
sure that the sectors are reallocated. If any remain, use the debugfs
method.  Of course the usual caveats apply - back it up first, and so
on.
                                                                                                                             
---------------------------------------------------------------------------

 

From: Frederic BOITEUX

HOW TO LOCATE AND REPAIR BAD BLOCKS ON AN LVM VOLUME

* Smartd reports an error in a short test?
-------------------------------------------

 

# smartctl -a /dev/hdb
...
SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed: read failure       90%        66         37383668

 

So the disk has a bad block located in LBA block 37383668

* In which physical partition is the bad block?
------------------------------------------------

 

# sfdisk -lu /dev/hdb

Disk /dev/hdb: 9729 cylinders, 255 heads, 63 sectors/track
Units = sectors of 512 bytes, counting from 0

 

   Device Boot    Start       End   #sectors  Id  System
/dev/hdb1            63    996029     995967  82  Linux swap / Solaris
/dev/hdb2   *    996030   1188809     192780  83  Linux
/dev/hdb3       1188810 156296384  155107575  8e  Linux LVM
/dev/hdb4             0         -          0   0  Empty

 

It's in the /dev/hdb3 partition, a LVM2 partition.
From the LVM2 partition beginning, the bad block has an offset of
(37383668 - 1188810) = 36194858

 

We have to find in which LVM2 logical partition the block belongs to.

* In which logical partition is the bad block?
-----------------------------------------------

 

*IMPORTANT*? LVM2 can use different schemes dividing its physical
 partitions to logical ones? linear, striped, contiguous or
 not... The following example assumes that allocation is linear?

 

The physical partition used by LVM2 is divided in PE (Physical Extent)
units of the same size, starting at pe_start' 512 bytes blocks from
the beginning of the physical partition.

 

The 'pvdisplay' command gives the size of the PE (in KB) of the
LVM partition?
#  part=/dev/hdb3? pvdisplay -c $part | awk -F: '{print $8}'
4096

 

To get its size in LBA block size (512 bytes or 0.5 KB), we multiply this
number by 2? 4096 * 2 = 8192 blocks for each PE.

 

To find the offset from the beginning of the physical partition is a
bit more difficult? if you have a recent LVM2 version, try?
# pvs -o+pe_start $part

 

Either, you can look in /etc/lvm/backup?
# grep pe_start $(grep -l $part /etc/lvm/backup/*)
                        pe_start = 384

 

Then, we search in which PE is the badblock, calculating the PE rank
in which the faulty block of the partition is?
physical partition's bad block number / sizeof(PE) =
36194858 / 8192 = 4418.3176

 

So we have to find in which LVM2 logical partition is used the PE
number 4418 (count starts from 0)?
# lvdisplay --maps |egrep 'Physical|LV Name|Type'
  LV Name                /dev/WDC80Go/racine
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    0 to 127
  LV Name                /dev/WDC80Go/usr
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    128 to 1407
  LV Name                /dev/WDC80Go/var
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    1408 to 1663
  LV Name                /dev/WDC80Go/tmp
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    1664 to 1791
  LV Name                /dev/WDC80Go/home
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    1792 to 3071
  LV Name                /dev/WDC80Go/ext1
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    3072 to 10751
  LV Name                /dev/WDC80Go/ext2
    Type                linear
    Physical volume     /dev/hdb3
    Physical extents    10752 to 18932

 

So the PE #4418 is in the /dev/WDC80Go/ext1 LVM logical partition.

* Size of logical block of filesystem on /dev/WDC80Go/ext1?
------------------------------------------------------------

 

It's a ext3 fs, so I get it like this?
# dumpe2fs /dev/WDC80Go/ext1 | grep 'Block size'
dumpe2fs 1.37 (21-Mar-2005)
Block size:               4096

 

* bad block number for the filesystem?
---------------------------------------

 

The logical partition begins on PE 3072?
 (# PE's start of partition * sizeof(PE)) + parttion offset[pe_start] =
 (3072 * 8192) + 384 = 25166208
512b block of the physical partition, so the bad block number for the
filesystem?is?
(36194858 - 25166208) / (sizeof(fs block) / 512)
= 11028650 / (4096 / 512)  = 1378581.25

 

* Test of the fs bad block?

 

dd if=/dev/WDC80Go/ext1 of=block1378581 bs=4096 count=1 skip=1378581

If this dd command succeeds, without any error message in console or
syslog, then the block number calculation is probably wrong? *Don't*
go further, re-check it and if you don't find the error, please
renunce?

 

* Search / correction follows the same scheme as for simple
  partitions?

 

- find possible impacted files with debugfs (icheck ,
  then ncheck ).

 

- reallocate bad block writing zeros in it, *using the fs block size*?

dd if=/dev/zero of=/dev/WDC80Go/ext1 count=1 bs=4096 seek=1378581

Et voil酄!

---------------------------------------------------------------------------

 

This document is version $Id: BadBlockHowTo.txt,v 1.9 2006/06/12 02:16:50 ballen4705 Exp $
It is Copyright Bruce Allen (2004-6) and distributed under GPL2.