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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next prev parent 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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