Messages in this thread | | | Date | Sat, 20 Mar 1999 07:01:28 -0500 (EST) | From | "Mark H. Wood" <> | Subject | Re: disk head scheduling |
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On Fri, 19 Mar 1999, Richard B. Johnson wrote: > On Fri, 19 Mar 1999, Arvind Sankar wrote: [much useful snippage] > > The real argument against doing all this is that it will save at most one seek > > per two requests, which is only 5% timewise. Probably not worth all the effort. > > > > The real argument against this is called "IDE". If you sorted reads > and writes (scatter/gather) for SCSI devices, you could accomplish > something.
A number of responses are all suggesting to me that what we really need is several different well-chosen scheduling strategies, and some reasonably good way to choose one for a particular drive, if we want to squeeze out the last drop of disk performance. Maybe as simple as:
if (disk is SCSI) { use bidirectional elevator merge reads and writes } else /* probably a dumb IDE drive */ { use one-directional elevator segregate reads and writes }
-- Mark H. Wood, Lead System Programmer mwood@IUPUI.Edu Remembering the day when disks were so primitive that each pack had a slotted ring which would interrupt a beam of light to inform the drive of the sector boundaries.
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