The SCAN-EDF strategy is a combination of the SCAN and EDF mechanisms.
The seek optimization of SCAN and the real time guarantees of EDF are combned in the follwoing way; like in EDF, the request with the earliest deadline is always served first, among
requests with the same deadline, the specific one that is first according to the scan direction is served first,, among the remaining requests, this principle is repeated until no request
with tis deadline is left.