EXT2 file system is the predecessor to the EXT3 file system. EXT2 is not journaled, and hence is not recommended any longer (customers should move to EXT3).
EXT3
Most popular Linux file system,
limited scalability in size and
number of files
Journaled
POSIX extended access control
EXT3 file system is a journaled file system that has the greatest use in Linux today. It is the "Linux" File system. It is quite robust and quick, although it does not scale well to large volumes nor a great number of files. Recently a scalability feature was added called htrees, which significantly improved EXT3's scalability. However it is still not as scalable as some of the other file systems listed even with htrees. It scales similar to NTFS with htrees. Without htrees, EXT3 does not handle more than about 5,000 files in a directory.
ReiserFS
Best performance and scalability when
number of files is great and/or files
are small
Journaled
POSIX extended access controls
The Reiser File System is the default file system in SUSE Linux distributions. Reiser FS was designed to remove the scalability and performance limitations that exist in EXT2 and EXT3 file systems. It scales and performs extremely well on Linux, outscaling EXT3 with htrees. In addition, Reiser was designed to very efficiently use disk space. As a result, it is the best file system on Linux where there are a great number of small files in the file system. As collaboration (email) and many web serving applications have lots of small files, Reiser is best suited for these types of workloads.
Since it's recommended anyway to have backups before filesystem conversions, you'd better copy everything (do not forget file permissions) somewhere, create an ext3 filesystem on that partition, then copy everything back.
Ext3 has been around since 2001 and is a logical extension of Ext2. Ext3 is regarded as being very reliable, and is available on virtually every Linux distribution. It's main feature is the ability to journal writes to the filesystem, allowing much faster crash recovery times, as there is no requirement to fsck the filesystem before mounting it.
Ext4 is a recent revision of Ext3, which adds the ability to store large (multi megabyte, ideally gigabyte) files more efficiently using an extend based layout. The expected benefit from using Ext4 over Ext3 would be a lower accounting overhead (less blocks on disk dedicated to filesystem metadata) and an increased throughput in sequential IO as extent based filesystems tend to group data physically together, reducing internal fragmentation.
Best Answer
Taken from: Linux Filesystem Primer
EXT2
EXT2 file system is the predecessor to the EXT3 file system. EXT2 is not journaled, and hence is not recommended any longer (customers should move to EXT3).
EXT3
EXT3 file system is a journaled file system that has the greatest use in Linux today. It is the "Linux" File system. It is quite robust and quick, although it does not scale well to large volumes nor a great number of files. Recently a scalability feature was added called htrees, which significantly improved EXT3's scalability. However it is still not as scalable as some of the other file systems listed even with htrees. It scales similar to NTFS with htrees. Without htrees, EXT3 does not handle more than about 5,000 files in a directory.
ReiserFS
The Reiser File System is the default file system in SUSE Linux distributions. Reiser FS was designed to remove the scalability and performance limitations that exist in EXT2 and EXT3 file systems. It scales and performs extremely well on Linux, outscaling EXT3 with htrees. In addition, Reiser was designed to very efficiently use disk space. As a result, it is the best file system on Linux where there are a great number of small files in the file system. As collaboration (email) and many web serving applications have lots of small files, Reiser is best suited for these types of workloads.