Confusing smartd messages

[Eugene Grosbein]

05.07.2018 7:54, George Mitchell write:

>> First step is running zpool scrub or even replace the disk and run "dd if=/dev/zero of=/dev/ada1".
>> [...]
> 
> I'll start with zpool scrub.  What's the magic command (if any) to
> force a rewrite of the sectors?                          -- George

Modern HDDs are embedded computers theyselves with their own CPU, RAM, flash memory
and special operating system (firmware) running inside. They have spare load
of generally unused and hidden sectors also. When firmware sees write error due
to really bad spot on magnetic part of disk making a sector "bad",
it performs a remap by means of internal translation table for LBAs
to use one of hidden sectors instead of bad one. And until the amount of hidden sectors
is not exhausted (there are can be over a thousand of them), the disk keeps running nearly fine.

Sometimes the sector just gets wrong checksum written due to power failure, hence read errors
due to "mismatched" checksum. Overwrite corrects such "soft bad" error without need to remap.

Eugene

P.S. your smtp server (MX) rejects my direct mail to you with "550 5.7.1 Access denied" errors.