From: Adam Borowski <kilobyte@angband.pl>
To: linux-btrfs@vger.kernel.org
Subject: Re: Does data checksumming remain for files with No_COW file attribute?
Date: Sun, 25 Sep 2016 01:50:14 +0200 [thread overview]
Message-ID: <20160924235014.GA2247@angband.pl> (raw)
In-Reply-To: <1498471474759532@web22g.yandex.ru>
On Sun, Sep 25, 2016 at 02:25:32AM +0300, Alexander Tomokhov wrote:
> Ok, so data checksumming does not remain for newly created empty files
> with No_COW attribute. I think it's an important trait of Btrfs behavior
> and should be added to wiki. So that users are informed that disabling
> CoW on a per-file basis also loses checksum correctness of such file.
Actually, it disables pretty much all btrfs features except for... CoW.
You lose:
* checksums
* compression
* safety against power loss (torn writes, etc)
* transactions (not that anyone uses them...)
* etc
But, CoW is still there. Try it: make a subvolume, create a FS_NO_COW file
(preferably one big enough), snapshot the subvolume, filefrag -v both
copies. Write to one of them, changing only a part of file. Wait for
writeout, filefrag -v them again.
--
An imaginary friend squared is a real enemy.
next prev parent reply other threads:[~2016-09-24 23:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-24 12:26 Does data checksumming remain for files with No_COW file attribute? Alexander Tomokhov
2016-09-24 12:37 ` Hugo Mills
2016-09-24 23:25 ` Alexander Tomokhov
2016-09-24 23:50 ` Adam Borowski [this message]
2016-09-25 5:44 ` Duncan
2016-09-26 20:41 ` Adam Borowski
2016-09-24 12:40 ` Roman Mamedov
2016-09-24 12:43 ` Hugo Mills
2016-09-24 18:11 ` Christoph Anton Mitterer
2016-09-25 13:49 ` Goffredo Baroncelli
2016-09-25 19:53 ` Christoph Anton Mitterer
2016-09-26 11:11 ` Austin S. Hemmelgarn
2016-09-24 18:09 ` Christoph Anton Mitterer
2016-09-24 21:44 ` Adam Borowski
2016-09-24 22:52 ` Christoph Anton Mitterer
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