From: Christoph Hellwig <hch@infradead.org>
To: device-mapper development <dm-devel@redhat.com>
Cc: DarkNovaNick@gmail.com,
LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] [dm-devel] [PATCH] dm snapshot: ignore discards issued to the snapshot-origin target
Date: Thu, 28 Apr 2011 03:53:55 -0400 [thread overview]
Message-ID: <20110428075355.GA2190@infradead.org> (raw)
In-Reply-To: <20110428001912.GA14659@redhat.com>
On Wed, Apr 27, 2011 at 08:19:13PM -0400, Mike Snitzer wrote:
> Discards pose a problem for the snapshot-origin target because they are
> treated as writes. Treating a discard as a write would trigger a
> copyout to the snapshot. Such copyout can prove too costly in the face
> of otherwise benign scenarios (e.g. create a snapshot and then mkfs.ext4
> the origin -- mkfs.ext4 discards the entire volume by default, which
> would copyout the entire origin volume to the snapshot).
You also need to make sure that we don't claim discard_zeroes_data for
the origin volume in this case. Especially as ext4 started to rely
on this actually working (very bad idea IMHO, but that's another story)
next prev parent reply other threads:[~2011-04-28 7:53 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-12 14:59 [linux-lvm] Testing TRIM with LVM DarkNovaNick
2011-04-12 23:47 ` Mike Snitzer
2011-04-13 1:47 ` DarkNovaNick
2011-04-13 8:41 ` Zdenek Kabelac
2011-04-13 15:38 ` DarkNovaNick
2011-04-13 22:40 ` [linux-lvm] [PATCH] dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM with LVM] Mike Snitzer
2011-04-13 23:48 ` [linux-lvm] " Mike Snitzer
2011-04-26 17:32 ` Mike Snitzer
2011-04-28 0:19 ` [linux-lvm] [PATCH] dm snapshot: ignore discards issued to the snapshot-origin target Mike Snitzer
2011-04-28 7:53 ` Christoph Hellwig [this message]
2011-04-28 20:59 ` [linux-lvm] do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target] Mike Snitzer
2011-04-28 21:28 ` Eric Sandeen
2011-04-28 22:59 ` Alasdair G Kergon
2011-04-28 23:01 ` Eric Sandeen
2011-04-28 23:11 ` Alasdair G Kergon
2011-04-29 1:12 ` Andreas Dilger
2011-04-29 13:55 ` Mike Snitzer
2011-04-29 9:30 ` Lukas Czerner
2011-04-29 12:24 ` [linux-lvm] [dm-devel] " Alasdair G Kergon
2011-04-29 12:29 ` Christoph Hellwig
2011-04-29 14:28 ` Eric Sandeen
2011-04-29 15:13 ` Ray Morris
2011-05-04 16:33 ` Ted Ts'o
2011-05-04 17:02 ` Lukas Czerner
2011-05-02 7:16 ` Lukas Czerner
2011-05-02 8:13 ` Alasdair G Kergon
2011-05-02 8:19 ` Christoph Hellwig
2011-05-02 10:24 ` Lukas Czerner
2011-05-02 12:48 ` [linux-lvm] " Mike Snitzer
2011-05-02 13:05 ` Lukas Czerner
2011-05-02 14:47 ` Eric Sandeen
2011-05-02 14:48 ` Christoph Hellwig
2011-05-02 14:58 ` Lukas Czerner
2011-05-02 13:48 ` [linux-lvm] [dm-devel] " Martin K. Petersen
2011-05-02 14:20 ` Martin K. Petersen
2011-05-02 14:39 ` Lukas Czerner
2011-05-02 14:50 ` Martin K. Petersen
2011-05-02 14:58 ` [linux-lvm] " Mike Snitzer
2011-05-02 16:58 ` [linux-lvm] [dm-devel] " Martin K. Petersen
2011-05-03 8:57 ` Lukas Czerner
2011-05-04 15:10 ` Martin K. Petersen
2011-05-04 16:02 ` [linux-lvm] " Mike Snitzer
2011-05-04 16:50 ` Martin K. Petersen
2011-05-04 18:03 ` Mike Snitzer
2011-05-04 17:10 ` [linux-lvm] [dm-devel] " Lukas Czerner
2011-05-04 17:32 ` Martin K. Petersen
2011-05-04 17:35 ` Lukas Czerner
2011-05-18 12:16 ` [linux-lvm] " Mike Snitzer
2011-05-18 12:52 ` Mike Snitzer
2011-05-04 15:16 ` [linux-lvm] [dm-devel] " Martin K. Petersen
2011-05-04 16:12 ` Lukas Czerner
2011-05-05 8:33 ` Karel Zak
2011-05-05 10:48 ` Lukas Czerner
2011-04-14 15:31 ` [linux-lvm] [PATCH] dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM wi DarkNovaNick
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