Disk Scheduling
Because disks are slow and seeks are long and depend on distance, we can schedule disk accesses, e.g.:
- FCFS (do nothing)
- ok when load is low
- long waiting times for long request queue
- SSTF (shortest seek time first)
- always minimize arm movement. maximize throughput.
- favors middle blocks
- SCAN (elevator) -- continue in same direction until done, then reverse direction and service in that order
- C-SCAN -- like scan, but go back to 0 at end
In general, unless there are request queues, it doesn’t matter
The OS (or database system) may locate files strategically for performance reasons.