There should be a mechanism that rearranges logical data blocks on the physical block device according to access patterns:

• Statistically evaluate access patterns.
• Rearrange blocks on the physical block device to optimize disk accesses.
• If there is enough free space on the physical device, one could even duplicate blocks to support multiple access patterns.

To be more explicit: this is not a defragmentation mechanism. It goes even further than that: in some situations it even fragments files in order to improve performance.