Update: Replacing hdparm --security-erase with hdparm --security-erase-enhanced allowed hexdump to read the entire drive on the next run, despite smartctl reporting no increase in reallocated sectors.
# fdisk -l /dev/sda
Disk /dev/sda: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
# hdparm --user-master u --security-erase p /dev/sda
security_password: "p"
/dev/sda:
Issuing SECURITY_ERASE command, password="p", user=user
# hexdump /dev/sda
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
hexdump: /dev/sda: Input/output error
4f5b1000
hexdump reports the offset in hexadecimal bytes. There are 512 bytes per sector on this drive as seen in step 0 above. Convert 4f5b1000 to decimal and divide by 512 to pinpoint the errant sector:
#echo $((0x4f5b1000))1331367936 #echo $((1331367936/512))2600328
# hexdump -s 1331367936 -n 1 /dev/sda
hexdump: /dev/sda: Input/output error
4f5b1000
(UPDATE: Using hexdump to display one of the last (simulated) sectors on an SSD took almost 13 minutes, while the dd and hdparm methods below were virtually instantaneous.)
# dd if=/dev/sda bs=512 skip=2600328 count=1 | hexdump
dd: error reading '/dev/sda': Input/output error
...
# hdparm --read-sector 2600328 /dev/sda
/dev/sda:
reading sector 2600328: succeeded
0000 0000 0000 0000 0000 0000 0000 0000
...
The hdparm man page states in part,
hdparm will issue a low-level read (completely bypassing the usual block layer read/write mechanisms) for the specified sector. This can be used to definitively check whether a given sector is bad (media error) or not (doing so through the usual mechanisms can sometimes give false positives).
However, these long-standing bugs may cause inaccurate results:
# hdparm --repair-sector 2600328 --yes-i-know-what-i-am-doing /dev/sda
/dev/sda:
re-writing sector 2600328: succeeded
Despite this seeming success, hexdump and dd still failed to read sector 2600328; skipping it resulted in their aborting on yet other read errors further on.
# for ((i=0;i<=3907029167;i++)) ; do hdparm --read-sector $i /dev/sda 2>&1 | grep FAILED ; done
reading sector 6305325: FAILED: Input/output error
...
That is: 1) iterate through all 3907029168 sectors, 2) read each sector with hdparm, 3) combine stderr and stdout (to keep the failed sector number and its error message together), and 4) look for lines containing "FAILED". Optionally, save output to fail.log while maintaining terminal output by adding |& tee -a fail.log after the grep command.
While this returns all unreadable sectors, it does not verify that all readable sectors contain zeros, which we can check by replacing grep with awk,
# for (( i=0; i<=3907029167; i++ )) ; do hdparm --read-sector $i /dev/sda 2>&1 ; done | awk '!/0000 0000 0000 0000 0000 0000 0000 0000/ && !/succeeded/ && NF && !/\/dev\/sda:/ || $4~/FAILED/'
excluding lines containing 32 zeros, "succeeded", nothing, and "/dev/sda:" (in order to return only any non-zero data), and printing lines containing "FAILED" in the fourth column.
Alas, after several days the process was still around two orders of magnitude away from completion.
# badblocks -b 512 -sv -t 0 -o bb.log /dev/sda
Checking blocks 0 to 3907029167
Checking for bad blocks in read-only mode
Testing with pattern 0x00: done
Pass completed, 615 bad blocks found. (615/0/0 errors)
# while read i ; do hdparm --repair-sector $i --yes-i-know-what-i-am-doing /dev/sda ; done <bb.log
All 615 sectors reported to have been rewritten successfully.
# while read i ; do hdparm --read-sector $i /dev/sda ; done <bb.log
A handful of unreadable sectors were still reported, but repairing then reading them individually (as many as 5 or 6 times in a few cases) succeeded at last.
How to get md RAID array to rebuild even if read errors for the hdparm for loop idea
user000001's answer to Brace expansion with variable? for the improved c-style for loop idea
slhck's answer to Send all error messages to a text file? for the STDERR to STDOUT redirect explanation
Byte Commander's answer to How do I save terminal output to a file? for the redirect table
repairbadblocks.sh for the badblocks and hdparm pairing idea
Bruno De Fraine's answer to Looping through the content of a file in Bash for the while loop idea
Is it possible to recover data from a drive overwritten with zeros once?
dd can optionally skip read errors via conv=noerror,sync
badblocks -wvs -c 16384 /dev/sdX will perform a destructive write-mode test to check for bad sectors, displaying progress and errors, and processing 16,384 blocks at a time (to avoid int32 limitations on larger-capacity drives).
created: 2018.06.02, updated: 2024.09.20