From mboxrd@z Thu Jan  1 00:00:00 1970
From: Brad Campbell <brad@fnarfbargle.com>
Subject: Re: Maximizing failed disk replacement on a RAID5 array
Date: Wed, 08 Jun 2011 15:32:26 +0800
Message-ID: <4DEF258A.8090600@fnarfbargle.com>
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To: Durval Menezes <durval.menezes@gmail.com>
Cc: linux-raid@vger.kernel.org, Drew <drew.kay@gmail.com>
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On 08/06/11 14:58, Durval Menezes wrote:

> 1) can I simply skip over these sectors (using dd_rescue or multiple
> dd invocations) when off-line copying the old disk to the new one,
> trusting the RAID5 to reconstruct the data correctly from the other 2

Noooooooooooo. As we stated early on, it you do that md will have no 
idea that the data missing is actually missing as the drive won't return 
a read error.

does a repair take long on your machine? I find that a few repair runs 
generally gets me enough re-writes to clear the dud sectors and allow an 
offline clone.

If your dd of the old disk to the new disk aborts with an error, do 
_not_ under any circumstances (well, unless you have really good 
backups) do a dd_rescue and just swap the disks.