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ext4 vs fsync, my take

Mar 17, 2009, 18:02 (1 Talkback[s])
(Other stories by Alexander Larsson)

"It should be noted that POSIX, and even ext4 gives no guarantees that the file will survive a system crash even if using fsync. For instance, the data could be outstanding in hardware buffers when the crash happens, or the filesystem in use may not be journaled or otherwise be robust wrt crashes. However, in case of a filesystem crash it gives a much better chance of getting the new data rather than the old, and on reordering filesystems like an unpatched ext4 it avoids truncated files from the rename method.

"Both the fsync and the non-fsync version has their places. For very important data the guarantees given by fsync are important enough to outweight the disadvantages. But in many cases the disadvantages makes it too heavy to use, and the possible data loss is not as big of an issue (after all, system crashes are pretty uncommon)."

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