ReiserFS Oracle Tips by Mike Ault

According to Daniel Robbins (drobbins@gentoo.org), President/CEO:

The ReiserFS 3.6.x (the version included as part of Linux 2.4) was designed and developed by Hans Reiser and his team of developers at Namesys. The ReiserFS uses a specially optimized b* balanced tree (one per filesystem) to organize all of its filesystem data. This offers a nice performance boost, as well as easing artificial restrictions on filesystem layouts. It's now possible to have a directory that contains 100,000 other directories, for example. Another benefit of using a b*tree is that ReiserFS, like most other next-generation filesystems, dynamically allocates inodes as needed rather than creating a fixed set of inodes at filesystem creation time. This helps the filesystem to be more flexible to the various storage requirements that may be thrown at it, while at the same time allowing for some additional space-efficiency.

ReiserFS also has a host of features aimed specifically at improving small file performance. Unlike ext2, ReiserFS doesn't allocate storage space in fixed one k or four k blocks. Instead, it can allocate the exact size it needs. And ReiserFS also includes some special optimizations centered around tails, a name for files and end portions of files that are smaller than a filesystem block. In order to increase performance, ReiserFS is able to store files inside the b*tree leaf nodes themselves, rather than storing the data somewhere else on the disk and pointing to it.

This does two things. First, it dramatically increases small file performance. Since the file data and the stat_data (inode) information are stored right next to each other, they can normally be read with a single disk IO operation. Second, ReiserFS is able to pack the tails together, saving a lot of space. In fact, a ReiserFS filesystem with tail packing enabled (the default) can store six percent more data than the equivalent ext2 filesystem, which is amazing in itself.

However, tail packing does cause a slight performance hit since it forces ReiserFS to repack data as files are modified. For this reason, ReiserFS tail packing can be turned off, allowing the administrator to choose between good speed and space efficiency, or opt for even more speed at the cost of some storage capacity.

Other Filesystems

Of course we also have many other filesystems such as those from Veritas, Polyserver and other specialized systems.

Oracle and Filesystems

Generally Oracle prefers filesystems that don’t do logging or journaling for filesystems that contain datafiles so if you use EXT2, EXT3 or reiserFS you need to mount them with the journaling or logging off. If RAW filesystems are used you avoid some overhead but usually can only obtain a 2-5 percent performance increase over modern optimized filesystems.

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