Re: Proactive Drive Replacement

[David Greaves <david@dgreaves.com>]

It is also worth saying that this has wandered way off topic.

The comment about parity rebuild yadda yadda was an aside to the real meat: a
drive replace facility that uses very efficient mirroring for >99.9% of the disk
rebuild and parity for the <0.1% where a read-error occured.

Hmm, it occurs in the event of a highly dodgy failed drive then maybe it could
do >99.9% recovery from parity and in the event of a failure from one of the
remaining drives, it could attempt a read from the dodgy disk.

David Lethe wrote:

> Sorry about rant .. but it got to me finally, where people keep posting
> how S.M.A.R.T. seems
> to be this all-knowing mechanism that tells you what is wrong with the
> disk and/or where the
> bad blocks might be.  It isn't.

No, but I run long self-tests on a weekly basis and when it tells me I have a
bad block I can examine further; attempt a re-write; run another long test and
see if it comes back clean.

David Lethe also wrote:
> As original poster wanted to just use SMART to factor in known bad
> blocks on a rebuild, then you can see that there
> Is no viable option unless you already have a full list of known bad
> blocks.  You have to find bad blocks as you
> just read from them as part of the rebuild for these types of disks).

I did say
 force a re-write of SMART identified badblocks using parity calculated values.
and that was innacurate.

I should have said something like:
  when SMART identifies a bad block then force a re-write using parity
calculated values.

I appreciate that SMART isn't that smart - but it has a lot of value way down
here below the top-end enterprise systems.

David
-- 
"Don't worry, you'll be fine; I saw it work in a cartoon once..."