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From: NeilBrown <neilb@suse.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Heinz Mauelshagen <heinzm@redhat.com>,
	device-mapper development <dm-devel@redhat.com>
Subject: Re: [PATCH] dm-raid: add RAID discard support
Date: Wed, 24 Sep 2014 09:33:08 +1000	[thread overview]
Message-ID: <20140924093308.120fe616@notabene.brown> (raw)
In-Reply-To: <yq18ulaszpk.fsf@sermon.lab.mkp.net>


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On Tue, 23 Sep 2014 19:07:35 -0400 "Martin K. Petersen"
<martin.petersen@oracle.com> wrote:

> >>>>> "Heinz" == heinzm  <heinzm@redhat.com> writes:
> 
> Heinz> In case of RAID levels 4,5 and 6 we have to check for the
> Heinz> capability to zero data on discards to avoid stripe data
> Heinz> corruption.
> 
> I'm quite concerned about relying on discard_zeroes_data since it's a
> hint and not a hard guarantee.
> 

If it is a "hint", then why isn't it "discard_sometimes_zeroes_data"?

md/raid5 already depends on this.  If a read from a discarded region doesn't
reliably return zeros, then raid5 cannot support discard.
Should I turn of discard support in raid5?

Also, could you help my understand when such a hint-but-no-guarantee would be
useful?

Thanks,
NeilBrown

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  reply	other threads:[~2014-09-23 23:33 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-23 16:51 [PATCH] dm-raid: add RAID discard support heinzm
2014-09-23 21:52 ` Brassow Jonathan
2014-09-23 23:07 ` Martin K. Petersen
2014-09-23 23:33   ` NeilBrown [this message]
2014-09-24  2:20     ` Martin K. Petersen
2014-09-24  4:05       ` Brassow Jonathan
2014-09-24  4:21         ` NeilBrown
2014-09-24  4:35           ` Brassow Jonathan
2014-09-24 11:02           ` Heinz Mauelshagen
2014-10-01  2:56             ` NeilBrown
2014-10-01 11:13               ` Heinz Mauelshagen
2014-10-03  1:12                 ` Martin K. Petersen
2014-10-01 13:32               ` Mike Snitzer
2014-10-01 23:34                 ` NeilBrown
2014-10-02  1:31                   ` Mike Snitzer
2014-10-02  2:00                     ` NeilBrown
2014-10-02  4:04                       ` [dm-devel] " NeilBrown
2014-10-02 13:52                         ` Mike Snitzer
2014-10-02 18:00                           ` Mike Snitzer
2014-10-03  1:14                         ` [dm-devel] " Martin K. Petersen
2014-10-01 16:00               ` [PATCH] " Andrey Kuzmin
2014-10-01 23:15                 ` NeilBrown
2014-10-01 18:57               ` Brassow Jonathan
2014-10-01 23:18                 ` NeilBrown
2014-10-03  1:09               ` Martin K. Petersen
2014-09-24 14:21   ` Christoph Hellwig
2014-09-24 14:38     ` Heinz Mauelshagen
2014-09-24 15:11     ` Martin K. Petersen

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