Data Security and Backup Versus Bad Sectors

June 10, 2017


I am thinking about getting a new, much larger data drive for backup, and reformatting my current drives as a BTRFS RAID mirror (0) array, so I have been doing some reading on the subject. Very interesting, heady stuff.

I think I’ll skip on the huge drive in favor of backing up data to a static DVD data store. Most of my stuff destined for backup is archival data, meaning it is static, not dynamic, and won’t change. Therefore, it will be fine to back that up to a static form, such as a closed DVD. (DVDs that are “open” can be “erased” and written-to again, allowing dynamic storage like a floppy disk, for a limited amount of time, until the overall data limit is used up by rewrites.) Backing up to DVDs will be more economical, because I already have in my possession the blank DVDs for the backup. I just haven’t made a lot of time for backups. (Bad me! Bad! Bad!) I plan to spend extra time with backing up data, by organizing the data in different ways. So the same data might be saved once to a “3D Flying Game” backup disk and to a “2D/3D CAD Drawing Programs and Data” backup disk also. This will not only create multiple backups (backups of backups), but will allow data to be more-easily found.

During my reading, I was reading about drive failures and sector failures. When a sector fails, the drive’s on-board processor marks the sector as bad and moves the data over to a known-good sector. Does it move it or does it copy it? That bad sector may contain the old data if it’s simply copied. Even if the drive “thinks” it moved that data, maybe the data might still be on the bad sector, if the drive was unable to “erase” the data after the move. This is entirely possible with failed physical bits.

Just because the current processor considers a sector bad, doesn’t mean that a disk restoration service or dumpster diver can’t replace the circuit board on the hard disk itself. When one controls that circuit board, one can access bad sectors. So if the data is only copied from bad sectors, and you think you have deleted your data when you dispose of your disk, someone might be able to restore that data. That sector might be insignificant, or it might have critical data. You won’t be the one to determine what is in that sector. So the bottom line is that you should never, ever sell your old disks, even formatted and thoroughly erased. You cannot be sure what can be recovered from that disk. So when you throw out a disk, be sure you drive a drill bit from top to bottom, or vice versa, to ensure that the physical disks inside are punctured and physically ruined.

It’s one thing to pull data from a disk that has failed. It’s almost completely unfeasible to pull data from a disk that has been punctured, splintered, and cracked. Even if it is put back together, just the back-together part of restoration can delete valuable bits of data, not to mention all the little shavings that were ripped from the physical disk during the drilling process. So yes, definitely make friends with your drill, and when it’s time to get rid of a drive, destroy it physically. Pickaxes, hammerclaws, and other puncturing tools are also fine for ruining physical disks.