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I have a drive in our iMac that has bad blocks, as booting from an Ubuntu 11.10 live CD and using ddrescue -f /dev/sda /dev/null finds them. I'd like to get the drive to remap them by writing to the blocks, say using hdparm --write-sector, but I don't want to do this without knowing what's in those blocks and finding the file that owns them, so I can restore the file from another source.

I found fileXray but don't feel like spending $79 to map a block to a file and hfsdebug has been taken offline. Are there suggestions on a tool or technique to use?

I looked at all the Ubuntu HFS+ packages to see if they could provide this info but nothing jumped out at me.

BTW, I used Disk Utility to erase the empty space, but it didn't get any of the bad blocks to be remapped, according to smartctl -A.

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  • Back it up with Time Machine, erase the disk, and reinstall.
    – gadgetmo
    Commented Feb 16, 2012 at 9:03

1 Answer 1

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If you are running Lion, man fsck_hfs and look at the -B option which says it will print files given a list of block numbers. Note: I had to include -n -f on the command to force a check, otherwise it just reported *** NO MATCH *** for all the blocks in my list.

Also, before attempting to overwrite a block, I'd want to develop and run some test to verify the mapping is correct between block numbers reported by ddrescue and those used by fsck_hfs and hdparm.

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    Passing -l to fsck_hfs seems like a safer way if the filesystem is currently mounted.
    – Blair Zajac
    Commented Oct 18, 2012 at 23:08
  • I also had to add -b 512 since, given a plain file (the output of ddrescue) it was unable to automatically determine a blocksize to work in. So, in total fsck_hfs -n -f -b 512 -B badblocks.txt <file>, where badblocks.txt was the hex offsets from the ddrescue map.txt divided by 512. Presumably one would also need to subtract off the offset of the start of the partition, but I had actually already done ddrescue on only one partition, rather than the whole raw device.
    – puetzk
    Commented Jan 7, 2023 at 7:47
  • > before attempting to overwrite a block, I'd want to develop and run some test to verify the mapping is correct I was also able to check this - I picked a file with fairly distinctive contents, and used grep --text --byte-offset 'whatever' partition.img, to find a plain byte offset where that data appeared. fsck_hfs correctly Identified the filename, so its block numbering is indeed just offset divided by 512 (or whatever -b <blocksize> was used).
    – puetzk
    Commented Jan 7, 2023 at 7:51

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