Overflow volume and segment settings are in the Output Preferences category.

When the disk volume to which After Effects is writing files is full, it can continue writing files to an overflow volume. You can set preferences to make After Effects render to up to six different disk volumes, as specified in the Overflow Volumes list. You can change the amount of disk space remaining on a volume before After Effects considers it an overflow by modifying the Minimum Diskspace Before Overflowing value.

After Effects can also render sequences and movie files into segments that are limited to a specified number of files or by file size; this is useful when preparing a movie for a medium such as CD-ROM, for which file or folder size may need to be limited to chunks of 650 MB or less. Use the Segment Movie Files At value to set the maximum size for segments in megabytes. Use the Segment Sequences At value to set the maximum number of still-image files in a folder.

Audio is also rendered in segments, the length of which is set by the Audio Block Duration value. If you hear pops in audio, you may be hearing a faulty transition between segments; if you have enough memory, increase the Audio Block Duration to be longer than your output to avoid this problem.