Doubt in OS: Disk scheduling

Question

In SCAN disk scheduling algorithm, we know that SCAN chooses the request that requires shortest seek distance in a preferred direction.

What direction SCAN chooses at the first place before servicing any request? Does it take any random direction or chooses in SSTF manner in the first place?

How do SCAN & C-SCAN suffer from indefinite postponement?

Answer 1

http://www.cs.iit.edu/~cs561/cs450/disksched/disksched.html