Hello, One important knob that can significantly change database disk IO is disk seek time. The disk model sent by Jim Gray suggested 4 msec seek time and transfer rate 250 MB/sec, and that is what I was using for estimating disk IO so far. Our local (SLAC) hardware experts tell me 4 msec is optimistic, and 6 msec would probably be more realistic (and it is unlikely to change any time soon). The transfer rate on the other hand is likely to go up because of the density growth. Unfortunately this does not seem to help much for the page sizes we consider (~128-256KB). The seek time change dominates, e.g. if I change seek time from 4 to 6 msec and triple the transfer rate, required number of disks increases almost proportionally to seek time increase (e.g. from from 6K to 9K).
So I think I will need a bit of guidance from TechAssessWG regarding what disk seek time I should assume for LSST for the year 2013. For convenience I'm attaching the disk model provided by Jim. thanks, Jacek
diskModel.xls
Description: MS-Excel spreadsheet
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