On 2017年08月14日 15:43, Paul Jones wrote:
-----Original Message-----
From: linux-btrfs-owner@xxxxxxxxxxxxxxx [mailto:linux-btrfs-
owner@xxxxxxxxxxxxxxx] On Behalf Of Qu Wenruo
Sent: Monday, 14 August 2017 4:37 PM
To: Christoph Hellwig <hch@xxxxxxxxxxxxx>; Christoph Anton Mitterer
<calestyo@xxxxxxxxxxxx>
Cc: Btrfs BTRFS <linux-btrfs@xxxxxxxxxxxxxxx>
Subject: Re: RedHat 7.4 Release Notes: "Btrfs has been deprecated" - wut?
On 2017年08月12日 15:42, Christoph Hellwig wrote:
On Sat, Aug 12, 2017 at 02:10:18AM +0200, Christoph Anton Mitterer wrote:
Qu Wenruo wrote:
Although Btrfs can disable data CoW, nodatacow also disables data
checksum, which is another main feature for btrfs.
Then decoupling of the two should probably decoupled and support for
notdatacow+checksumming be implemented?!
And how are you going to write your data and checksum atomically when
doing in-place updates?
Exactly, that's the main reason I can figure out why btrfs disables checksum
for nodatacow.
But does it matter if it's not strictly atomic? By turning off COW it implies you accept the risk of an ill-timed failure.
The problem here is, if you enable csum and even data is updated
correctly, only metadata is trashed, then you can't even read out the
correct data.
As btrfs csum checker will just prevent you from reading out any data
which doesn't match with csum.
Now it's not just data corruption, but data loss then.
Thanks,
Qu
Although from my point of view any reason that would require COW to be disabled implies you're using the wrong filesystem anyway.
Paul.
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