Using EXT2 on self powered HDD's is also advisable as it will increase the Read/Write speeds. As the major aging factor of a flash chip is the number of erase cycles, and as those happen frequently on writes, this increases the life span of the solid-state device.
EXT2 performs fewer writes than EXT3 since it does not need to write to the journal.
Also, if using any flash-based media (SD, Thumb drives, SSD etc., the EXT2 filesystem format is advised due to the fact that EXT3 uses Journaling. NOTE This Wiki applies only to USB capable devices. Formatting and Partitioning USB Storage for DD-WRT
