From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: write-refresh md array (feature request)
Date: Thu, 12 Sep 2013 09:05:48 +1000
Message-ID: <20130912090548.5613ab26@notabene.brown>
References: <20130910181905.GC21530@khazad-dum.debian.net>
	<CAA9_cmc+hJ9MrGyZDRXbUPNPcpgwm1RNvWQ4yX65zqKZy4puuQ@mail.gmail.com>
	<20130911123222.GA1736@khazad-dum.debian.net>
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To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Dan Williams <dan.j.williams@intel.com>, linux-raid <linux-raid@vger.kernel.org>
List-Id: linux-raid.ids

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On Wed, 11 Sep 2013 09:32:23 -0300 Henrique de Moraes Holschuh
<hmh@hmh.eng.br> wrote:

> On Tue, 10 Sep 2013, Dan Williams wrote:
> > On Tue, Sep 10, 2013 at 11:19 AM, Henrique de Moraes Holschuh
> > <hmh@hmh.eng.br> wrote:
> > > (please CC me on replies).
> > > I've been in several situations where it would have been helpful to b=
e able
> > > to refresh weak sectors by rewriting the whole md raid component devi=
ce,
> > > without the need to increase array failure risk through a fail+remove=
+add
> > > cycle for the component device.
> > >
> > > How difficult would it be to implement a "refresh" as a Linux md driv=
er
> > > sync_action, pigging back on "check" ?
> > >
> > > Are there any drawbacks to write-refreshing component devices?
> > >
> >=20
> > Why is "check" insufficient?  If it trips over any bad sectors it will
> > re-write them.
>=20
> The idea is to rewrite the sector _before_ it goes bad.
>=20
> Consumer SATA HDDs nowadays not only apparently fail to properly remap
> sectors because they don't track anymore that some sectors in that subtra=
ck
> were reported uncorrect a number of times (and thus are "weak").  They al=
so
> appear to not write-refresh sectors that required ECC correction, except
> maybe during an offline SMART test routine.
>=20

My view on this is that it has nothing to do with RAID.  If it is valuable =
to
"write-refresh" a device in a RAID array, then it would equally make sense =
to
write-refresh a device that wasn't in a RAID array.

So any solution to this should try to address the whole problem.

NeilBrown

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