There are a few other filesystem options for Linux that are not well enough explored for use with PostgreSQL:
- JFS: Performs similarly to XFS but with less CPU usage. However, it is considered less stable than the recommended choices here. It's also not as well supported by mainstream Linux distributors. Is it because it is not as well supported by mainstream Linux distributors that it gets less testing as a result, or are there fewer users because of the stability issues? Regardless, JFS was never very popular, and it seems to be losing ground now.
- ReiserFS: Being the first journaling filesystem integrated into the Linux kernel, for some time ReiserFS was the preferred filesystem for major Linux distribution, SuSE. Since SuSE abandoned it in late 2006 for ext3, ReiserFS adoption has been shrinking steadily since. At this moment, the current ReiserFS v3 is considered stable, but its replacement, ReiserFS v4, has yet to be merged with the mainline Linux kernel. The uncertain future of the filesystem limits interest in it considerably. This is unfortunate given that the transparent compression feature of ReiserFS v4 would be particularly valuable for some database workloads, such as data warehouses where large sequential scans are common.
- Btrfs: This Oracle-sponsored filesystem is considered the future of Linux filesystems even by the primary author of ext4. At this point, code development hasn't reached a stable release. At a future time when that does happen, this filesystem has some unique features that will make it a compelling option to consider for database use, such as its support for easy snapshots and checksums.
While each of these filesystems has some recognized use cases where they perform well compared to the more mainstream choices, none of these are considered compelling for database use in general, nor in PostgreSQL, due to maturity issues as this is being written. Btrfs in particular, may change in that regard as unlike the other two, it has a healthy development community working on it still.