Scheduling I/O

Lo scheduling I/O ("scheduling di input/output") è il metodo che i sistemi operativi utilizzano per decidere in quale ordine le operazioni di I/O richieste devono essere sottoposte al volume di immagazzinamento. Talvolta viene indicato con l'espressione disk scheduling.

Scopo

Seguono alcuni dei compiti principali dello scheduler I/O:

minimizzare il seek time, ovvero il tempo per posizionare la testina sulla traccia corretta;
dare priorità alle richieste di I/O di certi processi;
garantire equità, ovvero assicurarsi che il disco disponga di una banda per ciascun processo ed evitare il fenomeno di starvation.

Algoritmi

Fra gli algoritmi di scheduling più noti troviamo:^[2]

FCFS
Code di priorità
LIFO
Shortest seek first (SSF), o shortest seek time first (SSTF)
Algoritmo dell'ascensore (elevator algorithm), noto anche come SCAN, e le sue varianti:
- C-SCAN
- FSCAN
- N-Step-SCAN

Note

^ Werner Fischer e Georg Schönberger, Linux Storage Stack Diagram, su thomas-krenn.com, Thomas-Krenn AG, 28 ottobre 2014. URL consultato l'8 maggio 2015.
^ Gestione dei buffer e I/O scheduling (PDF), su dis.uniroma1.it, MIDLAB (Middleware Laboratory) - La Sapienza. URL consultato il 25 gennaio 2015 (archiviato dall'url originale il 23 febbraio 2005).

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