From: pinnerite@gmail.com   
      
   On Fri, 25 Jul 2025 10:01:09 -0400   
   Paul  wrote:   
      
   > On Fri, 7/25/2025 12:47 AM, Felix wrote:   
   > >   
   > > How does LM treat HD bad sectors? Can it identify and   
   > > mark them (if any) 'not for use'? or is there an app   
   > > that will do it? thanks all,   
   >   
   > https://askubuntu.com/questions/1127377/mark-ext4-blocks-as-ba   
   -manually-without-trying-to-read-write   
   >   
   > The problem I have with this idea, is later if you buy a   
   > new hard drive, and you want to clone over the drive (say using   
   > ddrescue), you would also copy the portion of the file system that declares   
   > some blocks bad. When cloning, the badblock information   
   > is really "private" to that particular drive.   
   >   
   > What you have to decide for yourself, is how far to push   
   > HDD, before transferring the data to a second drive.   
   >   
   > *******   
   >   
   > The hard drive has automatic sparing, which means if there   
   > is trouble with a sector, the drive has some spare sectors   
   > in the immediate area. And a table of spared blocks is   
   > maintained by the drive, independent of anything the user   
   > is doing. When the drive is getting low on spare sectors,   
   > the SMART "Reallocated" statistic raw data field goes non-zero,   
   > indicating drive life is on the warning track.   
   >   
   > The "smartctl" utility from smartmontools package, can tell   
   > you how healthy the drive is.   
   >   
   >     sudo smartctl -a /dev/sda   
   >   
   > SMART gives its best warnings, when the drive errors are   
   > independent of one another, and uniformly spread out. SMART   
   > gives a less-useful warning, when the drive has a "bad spot",   
   > as all the spares in the bad spot can be exhausted and yet   
   > the drive health will be declared as "Good".   
   >   
   > A bad spot in a disk, can be detected (and not all that accurately),   
   > by benchmark testing the disk with a transfer benchmark. For example,   
   > one drive I had, there was a 70GB wide area that transferred data   
   > at 10MB/sec (which is abnormally low). The drive health was listed   
   > as "Good" which is rubbish, as the drive was obviously not normal   
   > at that point. I transferred the data off the drive.   
   >   
   > *******   
   >   
   > Blocks with problems, are maintained in a queue for maintenance activity   
   > when an attempt is made to write the block. The drive will check whether   
   > the write is working or not, whether the block needs to be spared, it   
   > spares the block out and so on. This is all automated and may slow the   
   > drive down a bit while the determination is made.   
   >   
   > If you write the drive surface:   
   >   
   >     # Do a backup first, *before* the next command   
   >   
   >     smartctl -a /dev/sda   # Record health info before run begins.   
   >   
   >     sudo dd if=/dev/zero of=/dev/sda bs=221184   # Destructive write test   
   >   
   > Then do some reads:   
   >   
   >     sudo dd if=/dev/sda of=/dev/null bs=221184   # Read verify, test will   
   stop if bad block present   
   >   
   >     sudo ddrescue -f -n /dev/sda /dev/null /root/rescue.log   # Alternately,   
   ddrescue of gddrescue package can be   
   >     xed /root/rescue.log                                      # used to   
   generate a logfile with badblock info.   
   >                                                               # This   
   sequence differs from the previous command   
   >                                                               # in that the   
   command should always finish.   
   >   
   >     smartctl -a /dev/sda      # Look to see if Reallocated raw data   
   increased by a couple hundred,   
   >                               # indicating the questionable blocks have been   
   permanently harvested.   
   >                               # The raw data field might have a range of   
   0..5500 or so, just to give   
   >                               # some idea how worried you should be when   
   Reallocated = 300.   
   >   
   >     # Restore disk from backup once the harvesting is complete and you are   
   happy.   
   >   
   > But when the Reallocated SMART parameter raw data field goes non-zero,   
   > it is time to move the data off the disk and onto another disk.   
   > While you can punish a drive, use up all the spares in a region,   
   > forcing the drive to declare an actual "CRC error" on a block there,   
   > then you need to start using badblocks for EXT4 to manage the   
   > defects and keep the file system from using the now non-functional   
   > inodes. And if you do that, if you resort to manual badblock management,   
   > the main danger is accidentally transferring the (inaccurate for a second   
   > hard drive) badblock data to a new disk. You are really better off   
   > with the disks doing their own bad block management, and you the   
   > operator, monitoring SMART Reallocated plus watching for "benchmark   
   > bad spots" as indicators the drive is at end-of-life.   
   >   
   > *******   
   >   
   > The last hard drive I opened, a Seagate, I was shocked at what I found.   
   > The drive only had about 10,000 hours on it, when taken out of service.   
   > The Reallocated might have been 300. What did I find ? A single platter,   
   > which is to be expected on some of your hard drive fleet of course.   
   > What I didn't expect to find, is there was no landing ramp for the   
   > heads inside the drive. The head just sits on the platter. I looked it   
   > up, and after the "stiction era" (quantum fireball era or so), they   
   > had found a way to "laser pattern" the area near the platter hub and   
   > make a "non-stiction area" for the heads to park when the drive   
   > spins down. While modern lubricants (polymer finish) are fairly   
   > robust, not having a landing ramp for the head, that is just not a   
   > best practice, and guarantees if you cycle the power every day   
   > on the computer, the drive does lots of spinning down and wearing   
   > the heads as the heads skate over the surface.   
   >   
   > And that's why the drive had lasted only 10,000 hours. It was because   
   > even though the drives are in the modern era and science had discovered   
   > the benefits of landing ramps, my drive didn't have a plastic landing ramp.   
   >   
   > And this is just in case you do not understand why you didn't get   
   > 50,000 hours from a HDD. But you only figure things like this out,   
   > by examining the drive after it reaches end of life, to see whether   
   > the drive was too cheaply made. I never expected to find such an   
   > idiotic development, as to be dragging the heads across the platter   
   > when I opened the drive. I had expected to find dirt or rubbish inside   
   > the drive, proportional to a surface degradation, but the filter   
   > pack was still lilly white and the platter surface was impeccable   
   > to the eye, yet it had spared out enough blocks to be end-of-life.   
   > This means I'd need a microscope to find the damage that was   
   > present on the drive platter.   
   >   
   > *******   
   >   
   > When the first hard drives came out for consumers, I tested them   
   > in the lab. I took the factory bad block list, and the grown   
      
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