Les Mikesell wrote:
Roger Heflin wrote:
The big issue is that most of the smart implementations don't scan
the disk for bad blocks, and in my experience several years ago with
a 1000+ disks in services was that the #1 failure was bad blocks,
and smart did little to catch that. The #2 failure was failure to
spin up at all, but this seemed to be confined to certain batches.
Isn't that what the long surface scan test is supposed to do?
Probably. I started using dd test before disks and Linux and other
oses supported smart. It works on any disk (or array) whether smart
works or not.
That only catches 'hard' errors. Modern drives have spare sectors and
the ability to remap soft errors internally, up to a point, before the
OS knows anything about them. If the OS (or dd) sees an error, it means
you've used up the spares or the internal retries weren't able to fix
it. The smart interface is supposed to let you know far along you are
in using up the internal correction and how often soft errors are hidden
by the retries. It seems good in theory, and if it predicts the drive
is going bad you should probably believe it. But, I think a lot of
drives fail faster than the internal corrections can handle so you often
don't get any warning.
Yes, but dd will force the drive electronics to read the partially bad sector(s)
and then those same driver electronics will remap it if it decides it is bad
enough, you may not see an error, but the dd will have made the drive check the
sector. If you get a hard error, yes you are in trouble.
Roger
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