Journaling with ReiserFS
Mail servers tend to be a worst-case for the journaled file systems because they need to make sure each file operation completes. They use fsync, or a bunch of other tricks to prevent losing messages after a crash, and this forces the file system to close transactions while they are still very small.
Mail servers need a fast way to get new files committed to disk, and data logging can help with this. During the fsync call, you log the data blocks and metadata required to add the file in the tree, producing one large sequential write. If the file being written is a transient spool file, it might never be written back to the main drive. Combined with a fast dedicated logging device, data logging can make a big performance improvement.
As of yet, the ReiserFS 2.4 code does not support data logging. There is data logging code in our releases for the 2.2 kernels, but it needs to be adapted to the 2.4 page cache.
The end result of the new Linux file systems should be very interesting. Admins will be able to choose the best product for their applications, and programmers will be able to compare their decisions against the alternatives. Linux as a whole will benefit as the community picks and chooses the best features from each file system.
Chris Mason (email@example.com) was a system administrator before he started contributing to the ReiserFS Project. He now works full-time for SuSE from his home in Rochester New York.
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