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Alternate File Systems

The second extended file system, ext2, was developed by René Card as an alternative to the first file system derived from Minix. Although Linux supports many different file systems, ext2 remains the default for most distributions. Many vendors have improved on the default file system to offer features such as journaling, volume management, network block file systems, and shared disk file systems. Ext2 does not have these features built in.

Journaling File Systems

Enter the journal, the most popular alternative method to keep track of the file system. Depending on the implementation, journaling file systems use different methods based on a database to keep track of file system data. What's so attractive about journaling file systems is that fsck isn't needed. In the event of a system crash, the logs from the database can be replayed to represent the data at the time of a crash. This method tends to bring the system up to a consistent state much faster than a file system run with fsck; however, it doesn't do anything special for data reliability. A large RAID device that's using ext2 might take several hours to go through fsck checks, although with the addition of a journaling file system, no checks are made. All writes are made and played back from the journal, which results in a boot time of only minutes.

Different journaling file systems also have support for synchronous I/O, increased block size support, integration with NFS, quota support, and support for access control lists (ACLs).

Network File Systems

Network file systems manage to take one or more devices and appear to the server as one logical volume. The trick here is to fool the OS into thinking that the volume is a locally attached RAID or clustered device. The network file system naturally shows some performance loss due to the network overhead.

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