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Date: Thu, 5 Jul 2018 19:03:30 +0200 (CEST)
From: Wojciech Puchar <wojtek@puchar.net>
To: Alan Somers <asomers@freebsd.org>
cc: Stefan Blachmann <sblachmann@gmail.com>,
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 Lev Serebryakov <lev@freebsd.org>, Wojciech Puchar <wojtek@puchar.net>
Subject: Re: Confusing smartd messages
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>
> Rewriting suspicious sectors is useless in this day and age.  HDDs and SSDs
> already do it internally and have for years.  Even healthy sectors get

unreadable sectors cannot be rewritten by drive electronics as 
it doesn't know what to rewrite. it may possibly remap it but still report 
read error until some data will be written - unless giving no error and 
returning meaningless data is an accepted behaviour.

only on write it can be done properly.

> that the HDD/SSD won't fix itself would be a checksum error.  Those are

yes and this will happen if you powerdown your disk on write. or get some 
power spike or other source of noise that would affect electronic 
components.

performing full disk rewrite (so not zfs rebuilds) and THEN looking at 
smart stats and THEN performing regular smartctl -t long will tell the 
truth.

which usually is "drive is fine" in my practice. really faulty drive will 
QUICKLY develop new problems.