Re^2: Efficiency of seek

that deferring reads and re-ordering them could reduce head movement and improve throughput, but most disk controllers do this as a matter of course now

That is impossible unless the application uses some kind of asynchronous IO in order to queue several read operations and let the OS/hardware handle them in some order that minimizes head movement delays.

But for common applications using synchronous IO, the app will ask for some data, wait for the OS to fulfill the request, ask for some other data, etc., so there is no way for the OS to reorder the operations.

Another matter is considering a multithreaded/multiprocess environment where the OS/hardware can reorder the IO operations queued at any point in time by all the running threads.

Comment on Re^2: Efficiency of seek

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Re^3: Efficiency of seek by BrowserUk (Patriarch) on Sep 01, 2011 at 16:25 UTC
That is impossible ... Look up the SCAN and C-SCAN algorithms. Start here... Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^4: Efficiency of seek by salva (Canon) on Sep 01, 2011 at 19:42 UTC
SCAN, C-SCAN and for that matter any other algorithm (besides those using a crystal ball to see into the future) are useless for mono-threaded applications doing synchronous read operations. Think about it!	[reply]
Re^5: Efficiency of seek by BrowserUk (Patriarch) on Sep 01, 2011 at 20:06 UTC
Why are you making such a big deal about a passing comment? are useless for mono-threaded applications A few thoughts: Did I suggest otherwise? (Hint: NO!) Do you run all your programs on dedicated systems with no other processes (system or user) running? Cos if not, your disk accesses are probably benefiting from disk scheduling algorithms as we speak. What do you know about RK05 disk packs mounted for dedicated use? How about BasicPlus virtual arrays? Perhaps you don't know as much as you think. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]