On Tue, Jun 11, 2013 at 02:17:16PM -0500, Steve Bergman wrote: > Now about ext3 behavior. (Sorry, I know this is an XFS list, but I've > been dying to have this clarified. And this does kind of relate to > XFS.) Not only does data get flushed more frequently. But it gets > careful treatment. It gets written out immediately before the > metadata. That's not careful treatment, that's just ordering. XFS has "careful treatment", too, but it orders data and metadata differently. XFS doesn't actually update the inode size until after the data is written i.e. the size is still zero until the data is written. That's how XFS orders data vs metadata updates - metadata that is oly valid after data IO completes is not modified until after the data IO completes... Hence if you create a file, write some data and then crash before the data is written, you'll get the create replayed but nothing else. i.e. a zero length file. Often it is just the inode size transaction that is missing from the log - the data is actually on disk and *can be recovered* if you know what you are doing... IOWs, the thing that causes people to complain about XFS and zero length files is that XFS leaves *observable evidence* of data loss behind, while ext3 and ext4 don't. Hence when people switch to XFS they actually notice (maybe for the first time!) that running their laptop battery dead leads to data loss and that their applications are not behaving safely. They then shoot the messenger (i.e XFS) for losing data as ext3/ext4 don't "lose data" as they don't leave any observable evidence of partial file states... Filesystems behave differently, but those observable differences in behaviour don't mean one filesystem loses more data than another. Some filesystems just makes it easier to find evidence of such data loss and hence make it easier to recover from, not to mention make it obvious which applications write data unsafely and hence shouldn't be trusted.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
