The block layer

Perhaps the most radically changed component

Themes:
De-crufting
No more global arrays
Partition handling moved out of drivers
Scalability
No more io_request_lock
Supporting 4000 disks on one system
64-bit sector numbers
Performance
Large requests stay intact
Direct and asynchronous I/O
Features
Drive diagnostic and power mgmt commands
Pluggable elevators (I/O schedulers)