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Date:      Thu, 27 Jun 2013 10:06:45 -0700
From:      Charles Swiger <>
To:        Adam Vande More <>
Cc:        =?utf-8?Q?Nikola_Pavlovi=C4=87?= <>, FreeBSD Questions <>
Subject:   Re: Troubleshooting a gmirror disk marked broken
Message-ID:  <>
In-Reply-To: <>
References:  <20130627023837.GA7685@sputnjik.localdomain> <> <>

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On Jun 27, 2013, at 9:58 AM, Adam Vande More <> =
> On Thu, Jun 27, 2013 at 10:16 AM, Charles Swiger <> =
>> If you haven't rebuilt the mirror already, running a full disk read =
>> against both drives (ie, via "dd if=3D/dev/ad4 of=3D/dev/null bs=3D1m" =
or similar)
>> might be prudent.  That will help identify/migrate any sectors which =
>> failing but still recoverable via ECC to the spare sectors.
> I was going to say something like that too but AFAIK sectors aren't =
remapped on failed reads, has to be written to(dd if=3D/dev/zero =
of=3D/dev/ad4 bs=3D1m).  If it were me, I make sure I had fully tested =
complete backups before I broke the mirror and did that.

If the drive reads a sector with ECC-correctable errors, it's supposed =
to try to re-write that sector in order to fix up the ECC data.  If that =
write fails, it remaps.

Of course, your suggestion of blanking the entire drive and restoring =
from the mirror or a backup would be best, or perhaps "better short of =
replacing the drive".


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