In this section we'll briefly describe the enhanced filesystem that has evolved from Ext2, named Ext3. The new filesystem has been designed with two simple concepts in mind:
• To be a journaling filesystem (see the next section)
• To be, as much as possible, compatible with the old Ext2 filesystem
Ext3 achieves both the goals very well. In particular, it is largely based on Ext2, so its data structures on disk are essentially identical to those of an Ext2 filesystem. As a matter of fact, if an Ext3 filesystem has been cleanly unmounted, it can be remounted as an Ext2 filesystem; conversely, creating a journal of an Ext2 filesystem and remounting it as an Ext3 filesystem is a simple, fast operation.
Thanks to the compatibility between Ext3 and Ext2, most descriptions in the previous sections of this chapter apply to Ext3 as well. Therefore, in this section, we focus on the new feature offered by Ext3 — "the journal."
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