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  • "When a sector is written, it is immediately read back" -- Not true. Such an operation is called "write-then-read" or "write verification", and is not a standard write operation (because such an extended operation requires another revolution of the platter).
    – sawdust
    Commented Oct 25, 2016 at 22:57
  • Wow, really, it isn't on by default? Crap, I'm going to go figure out how to enable that. It seems fairly obvious.
    – enigmaticPhysicist
    Commented Oct 26, 2016 at 6:01
  • "It seems fairly obvious" -- Only if you're paranoid. You probably don't even know what kind of write caching policy is employed in your HDD. See Write Caching. IOW your OS could be notified that the write operation is successfully complete before the the sector has been actually written, much less verified.
    – sawdust
    Commented Oct 26, 2016 at 8:32
  • Here's a patent for the (integrated) disk controller to automatically perform a read-after-write. Look for the paragraph near the end that starts with "There is a performance cost associated with this RVaW feature..." that validates my first comment. I have no idea if any HDD actually uses this scheme.
    – sawdust
    Commented Oct 26, 2016 at 8:46
  • I just remembered these hard drives also use error correction. That's how they can get away with it. Very interesting. And I know about caching, BTW.
    – enigmaticPhysicist
    Commented Oct 26, 2016 at 19:45