1. Purpose

At this point, we are trying to logically connect a filesystem (a local partition or a server volume) with the directory tree. The filesystem can be located anywhere.

The following situation is not uncommon:

• You have a large directory, say /home/jack, which is getting bigger and bigger.
• You are out of disk space.
• You buy a second hard drive, create a single partition on it (/dev/hdb1 for example).
• You rename /home/jack to /home/jack.backup
• You map /dev/hdb1 to /home/jack.
• You copy /home/jack.backup to /home/jack.

After that, you may delete /home/jack.backup. You get the same logical file layout, but now have space on the first drive and a lot of space for /home/jack to grow on the second.