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Date: Sun, 29 Mar 2009 12:24:21 +0200 From: Alberto Gonzalez <info@...bu.es> To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Ext4 and the "30 second window of death" Hi, Reading this discussion about the fsync performance problems, the reliability of delayed allocation, etc... made me a bit confused, so as a normal user I would like to ask a clear question with an example so I can get a clear answer and understand the implications of all this. - Let's say I'm a writer and I like to take my laptop to a cafe every day to write there for a few hours. - As such, I want to get good battery life so I'm fine with my data being written to death say every 30 seconds instead of waking up the disk immediately if I save the document I'm working on. - I use Ext4 as my filesystem (default in next Fedora release). - Let's say I've been working on my book for the last 14 months and I've written about 400 pages on an ODF file. - My usual workflow is that every time I finish a paragraph, say every 2-3 minutes, I hit Ctrl+S to save the changes. - So one day, while I'm working on the book the following happens: I finish a paragraph and his Ctrl+S to save it. 5 seconds later the system freezes for some reason. Let's suppose that in that 5 window timeframe between pressing Ctrl+S and the crash the data has not been written to disk (which happens every 30 seconds). So as a result I: A - Lose that last paragraph B - Lose the whole book If it's 'A', then that's ok, as expected. Bad luck. But if it's 'B', then I think that's totally unexpected by any user, and totally unacceptable too. Sure I want good performance and good battery life, but not at such cost. (Yes, you can argue I should have a recent backup at home, and you'd be right, but that doesn't change things fundamentally). As far as I understand, with Ext3 (defaults), the behavior was A. Will this change to B with Ext4 and all "modern" filesystems (XFS, Btrfs,...)? Thanks for any answer. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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