From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jakob Unterwurzacher Subject: Re: Rename+crash behaviour of btrfs - nearly ext3! Date: Tue, 18 May 2010 14:03:49 +0200 Message-ID: <4BF28225.2000908@gmail.com> References: <4BF18525.8080904@gmail.com> <20100517193652.GC8635@think> <4BF1DBCD.7060208@gmail.com> <20100518003032.GK8635@think> <20100518005926.GM8635@think> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: Chris Mason , linux-btrfs@vger.kernel.org Return-path: In-Reply-To: <20100518005926.GM8635@think> List-ID: On 18/05/10 02:59, Chris Mason wrote: >>> Ok, I upgraded to 2.6.34 final and switched to defconfig. >>> I only did the rename test ( i.e. no overwrite ), the window is now >>> 1.1s, both with vanilla and with the patch. >> >> Thanks, so much for the easy fix. I'll take a look. > > Ohhhhh, I read your initial email wrong, I'm sorry. The test we're > failing, the rentest, doesn't overwrite one file with another. It is > just creating a file and then renaming it. Yes, the overwrite test goes perfectly fine. > Btrfs is explicitly choosing not to sync the file in this case because > the rename isn't replacing good old data with new unwritten data. The > rename is taking new unwritten data and giving it a different name. > > Are there applications that rely on this? > > -chris Well, dpkg (the Debian/Ubuntu package manager) did. Then ext4 became the default fs in Ubuntu and massive breakage was reported [1]. Now dpkg is fsync()ing everything and is about 2x slower than it was with ext3 [2]. Btrfs is so close to getting it "right" that i wondered whether the new file name hitting the disk could be delayed that one second for the data to make it to disk first. Anyway, btrfs is still a factor 30 better than ext4 of xfs! Thanks, Jakob [1] https://bugs.launchpad.net/ubuntu/+source/dpkg/+bug/512096 (notice the massive duplicate list on the right!) [2] https://bugs.launchpad.net/ubuntu/+source/dpkg/+bug/537241