> From: Charles Polisher [mailto:[email protected]] > > There's a tradeoff between how fast the designer wants the head > to seek and how much heat they're willing to dissipate in the > positioning servo. With infinite power you can position the > head pretty damn fast.
A good point - I have neither data to confirm or deny any difference in average seek time of 2.5" vs 3.5" disks, but I have the presumed position that they're approximately equal. If this is correct, it could be explained as you said - the larger disks have more distance to travel, but also have more power and cooling available. > If you consider groups of disks, rotational latency isn't > completely governed by RPMs. Two mirrored disks can be written > 180 degrees out of phase with 50% of the rotational latency of a > single disk, 4 disks can be stepped at 90 degrees delivering a > quarter the latency, etc. This is true, but not practical. Besides the fact that rotational latency is a slim slim minority of where time is lost - the head seek time is where the vast majority of ground to be gained - There are techniques such as short-stroking to minimize head seek. But just like short-stroking, if you have tuned drivers and just a teeny little bit of proprietary hardware support, you can get knowledge about the rotational position of head over platters, and the variations of sector density according to track position, and you can keep your volatile data in a tightly grouped small number of tracks (or rotating buffer or similar) so you can get IOPS out of a HDD that are comparable to SSD. But because it's a specialized function, these types of performance enhancements are pretty well limited, practically, to the academic world. The cost differential (as well as other characteristics) between SSD, vs Hybrid, vs HDD does not provide significant enough motivation for manufacturers to productize commercial offerings of this type... _______________________________________________ Discuss mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
