You might have read that ext2/ext3 has support for so called "directory indexes", which supposedly speed up operations on directories with many files. For example your /usr/share/doc directory, your packages database, or your home directory (use ls -la | wc -l to count the number of files).

However, this feature is not enabled on most machines, since up to now you needed to pass a flag when creating the filesystem. The 1.39 upload of e2fsprogs (in Debian unstable as of May 29) made this default. So you probably didn't enable this when creating your filesystem.

To check, first find out what your filesystem device is (use mount). Mine is /dev/hda5, so my example will use this device. In traditional terms, this is the first extended partition on the IDE primary master drive.

Now use tune2fs -l /dev/hda5 | grep features to get a list of your filesystem features. If you have "dir_index" in there then you're all set. Ignore any "needs_recovery" - that is good for mounted filesystems (it just means "not cleanly unmounted")

To add dir_index, do the following.

• Unmount the filesystem. If this is your primary filesystem, use a bootable CD like Knoppix or some Linux install CD.
• Make sure the filesystem is really not mounted. Just for safety of your data. Run e2fsck /dev/hda5 - this should take less than one second if your filesystem is clean and is needed anyway otherwise...
• Execute tune2fs -O +dir_index /dev/hda5 to enable the feature for your filesystem
• Execute e2fsck -Df /dev/hda5. This will force a filesystem check with directory optimization (!) on your filesystem.
• Mount your system (or reboot, if you were using a live CD)