From: Austin S Hemmelgarn <ahferroin7@gmail.com>
To: Jonathan Panozzo <jonp@lime-technology.com>,
Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: Chris Murphy <lists@colorremedies.com>,
Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: Questions on use of NOCOW impact to subvolumes and snapshots
Date: Thu, 20 Aug 2015 08:09:26 -0400 [thread overview]
Message-ID: <55D5C376.9090809@gmail.com> (raw)
In-Reply-To: <540B3004-C250-4C21-9E53-C38E20258DA9@lime-technology.com>
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On 2015-08-20 00:40, Jonathan Panozzo wrote:
> Zhao,
>
> Thank you for your response. Two quick follow-up questions:
>
> 1: What happens on an unrecoverable data error case? Does the volume get put into read-only mode?
Yes.
>
> 2: Out of curiosity, why is data checksumming tied to COW?
There's no safe way to sanely handle checksumming without COW, because
there is no way (at least on current hardware) to ensure that the data
block and the checksums both get written at the exact same time, and
that one of the writes aborting will cause the other too do so as well.
In-place compression is disabled for nodatasum files for essentially
the same reason (although compression can cause much worse data loss
than a failed checksum).
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next prev parent reply other threads:[~2015-08-20 12:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-20 0:44 Questions on use of NOCOW impact to subvolumes and snapshots Jonathan Panozzo
2015-08-20 1:55 ` Chris Murphy
2015-08-20 3:43 ` Russell Coker
2015-08-20 16:44 ` Chris Murphy
2015-08-20 17:31 ` Austin S Hemmelgarn
2015-08-20 4:09 ` Zhao Lei
2015-08-20 4:40 ` Jonathan Panozzo
2015-08-20 6:03 ` Zhao Lei
2015-08-20 6:13 ` Jonathan Panozzo
2015-08-20 6:31 ` Zhao Lei
2015-08-20 12:09 ` Austin S Hemmelgarn [this message]
2015-08-21 3:34 ` Russell Coker
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