File System Types
Individual drive partitions can be setup using one of the many different available filesystems. Each has its own advantages, disadvantages, and unique idiosyncrasies. A brief overview of supported filesystems follows; the links are to wikipedia pages that provide much more information.
- ext2 Second Extended Filesystem is an established, mature GNU/Linux filesystem that is very stable. A drawback is that it does not have journaling support (see below) or barriers. Lack of journaling can result in data loss in the event of a power failure or system crash. It may also be inconvenient for root (
/homepartitions because file-system checks can take a long time. An ext2 filesystem can be converted to ext3.
- ext3 Third Extended Filesystem is essentially the ext2 system with journaling support and write barriers. It is backward compatible with ext2, well tested, and extremely stable.
- ext4 Fourth Extended Filesystem is a newer filesystem that is also compatible with ext2 and ext3. It provides support for volumes with sizes up to 1 exabyte (i.e. 1,048,576 terabytes) and files sizes up to 16 terabytes. It increases the 32,000 subdirectory limit in ext3 to 64,000. It also offers online defragmentation capability.
- ReiserFS (V3) Hans Reiser's high-performance journaling FS uses a very interesting method of data throughput based on an unconventional and creative algorithm. ReiserFS is touted as very fast, especially when dealing with many small files. ReiserFS is fast at formatting, yet comparatively slow at mounting. Quite mature and stable. ReiserFS (V3) is not being actively developed at this time. Generally regarded as a good choice for
- JFS IBM's Journaled File System was the first filesystem to offer journaling. It had many years of development in the IBM AIX® operating system before being ported to GNU/Linux. JFS makes the smallest demand on CPU resources of any GNU/Linux filesystem. It is very fast at formatting, mounting, and filesystem checks (fsck). JFS offers very good all-around performance especially in conjunction with the deadline I/O scheduler. It is not as widely supported as the ext series or ReiserFS, but still very mature and stable.
- XFS is another early journaling filesystem originally developed by Silicon Graphics for the IRIX operating system and ported to GNU/Linux. It provides very fast throughput on large files and filesystems and is very fast at formatting and mounting. Comparative benchmark testing has shown it to be slower when dealing with many small files. XFS is very mature and offers online defragmentation capability.
All the above filesystems with the exception of ext2 use journaling. Journaling provides fault-resilience by logging changes before they are committed to the filesystem. In the event of a system crash or power failure, such file systems are faster to bring back online and less likely to become corrupted. The logging takes place in a dedicated area of the filesystem.
Not all journaling techniques are the same. Only ext3 and ext4 offer data-mode journaling, which logs both data and meta-data. Data-mode journaling comes with a speed penalty and is not enabled by default. The other filesystems provide ordered-mode journaling, which only logs meta-data. While all journaling will return a filesystem to a valid state after a crash, data-mode journaling offers the greatest protection against corruption and data loss. There is a compromise in system performance, however, because data-mode journaling does two write operations: first to the journal and then to the disk. The trade-off between system speed and data safety should be considered when choosing the filesystem type.