zemerdon.com

Posted: **Tue Jan 16, 2024 2:46 pm**

https://wiki.archlinux.org/title/Identify_damaged_files

Force the disk to reallocate bad block
First you will want to see how many badblocks the harddrive is aware of through the smartctl command:

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# smartctl -t long /dev/sdx

Wait until test completes, then:

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# smartctl -l selftest /dev/sdx

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

To make the harddrive transparently map out the badblock with a spare good sector you will have to simply write zeros to the bad block using the dd command as root. Remember that with this command you have to work with the same block size as your filesystem and the block has to be relative to the partition the filesystem is on and not the harddrive as a whole:

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dd if=/dev/zero of=/dev/sdxy bs=4096 count=1 seek=2269012 sync

Alternatively, hdparm provides a couple of nice and simple options to read and write a given sector (4621327, in the following example):

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hdparm --read-sector 4621327 /dev/sdxy
hdparm --repair-sector 4621327 --yes-i-know-what-i-am-doing /dev/sdxy

You can see if the harddrive did indeed map out an additional bad sector by checking with the smartctl command and seeing if the reallocated sector or event count went up:

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# smartctl -A /dev/sdx

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
To get Offline_Uncorrectable to go back to 0 you need to run a SMART long test and a selftest:

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smartctl -t long /dev/sdx

Wait until test completes, then:

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smartctl -l selftest /dev/sdx

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ZFS HDD force write bad sectors