Hi Jacek, If the seek time is that significant, perhaps we should model this as a trend over time rather than a point.
Jeff > From: Jacek Becla <[EMAIL PROTECTED]> > Organization: Stanford Linear Accelerator Center > Reply-To: LSST Data Management <[email protected]> > Date: Thu, 06 Jul 2006 13:09:36 -0700 > To: LSST Data Management <[email protected]> > Cc: Don Dossa <[EMAIL PROTECTED]> > Subject: [LSST-data] disk seek time? > > 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 > > _______________________________________________ > LSST-data mailing list > [email protected] > http://www.lsstmail.org/mailman/listinfo/lsst-data > _______________________________________________ LSST-data mailing list [email protected] http://www.lsstmail.org/mailman/listinfo/lsst-data
