The ext3 file system is an enhanced version of the ext2 file system.
The most important difference between ext2 and ext3 is that ext3 supports journaling.
After an unexpected power failure or system crash (also called an unclean system shutdown), each ext2 file system must be checked for consistency by the e2fsck program. This is a time-consuming process and during this time, any data on the volumes is unreachable.
The journaling provided by the ext3 file system means that this sort of a file system check is no longer necessary after an unclean system shutdown. The only time a consistency check occurs while using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to recover an ext3 file system after an unclean system shutdown does not depend on the size of the file system or on the number of files. Rather, it depends on the size of the journal used to maintain consistency. The default journal size takes almost a second to recover, depending on the speed of the hardware.