Quick reminder for myself on how to fix unreadable sectors on a disk. Doing this live is possible on a zfs pool for example (or probably other RAID setups that have redundancy) but otherwise it is safer to unmount the disk/partition first.
Here are the errors reported by SMART:
Device: /dev/sdb [SAT], 8 Currently unreadable (pending) sectors
Device: /dev/sdb [SAT], 8 Offline uncorrectable sectors
First run a full Extended offline test:
$ smartctl -t long /dev/sdb
Once the test is done, check the results:
$ smartctl -a /dev/sdb
...
Sector Sizes: 512 bytes logical, 4096 bytes physical
...
# 9 Extended offline Completed: read failure 30% 19394 2776811256
....
The bad sector then need to be zeroed out (adapt the bs argument with the sector sizes
and the seek with the first bad sector offset reported from the above command):
$ dd if=/dev/zero of=/dev/sdb bs=512 count=1 seek=2776811256 conv=noerror,sync
$ sync
Repeat the above procedure until all bad sectors have been fixed. At the end, make sure no more bad sectors are detected with:
$ smartctl -A /dev/sdb | grep Offline_Uncorrectable
198 Offline_Uncorrectable 0x0010 100 100 000 Old_age Offline - 0
References:
- http://bytesandbolts.com/fixing-freenas-error-currently-unreadable-pending-sectors/
- http://linoxide.com/linux-how-to/how-to-fix-repair-bad-blocks-in-linux/
- https://dekoder.wordpress.com/2014/10/08/fixing-freenas-currently-unreadable-pending-sectors-error/
EDIT
I experienced that sometimes dd is unable to write to a bad sector, resulting in a similar output
dd: error writing ‘/dev/sdb’: Input/output error
The workaround is to use hdparm in order to fix it
# read the bad sector to validate it is indeed bad
$ sudo hdparm --read-sector 2757742944 /dev/sdb
/dev/sdb:
reading sector 2757742944: FAILED: Input/output error
# write to it
$ sudo hdparm --write-sector 2757742944 --yes-i-know-what-i-am-doing /dev/sdb
/dev/sdb:
re-writing sector 2757742944: succeeded
# re-read to confirm it is fixed
$ sudo hdparm --read-sector 2757742944 /dev/sdb
/dev/sdb:
reading sector 2757742944: succeeded
...
Smartctl then shows that one sector was reallocated:
$ sudo smartctl -a /dev/sdb | grep -i reallocated
5 Reallocated_Sector_Ct 0x0033 100 100 010 Pre-fail Always - 1
References: