On Wed, Feb 19, 2014 at 04:08:28PM +0000, Edward Ned Harvey (lopser) wrote: > > From: Adam Levin [mailto:[email protected]] > > > > While this is the first time I've ever heard that 7.2k benchmark the same as > > 15k, I do know that 10k 2.5" benchmark nearly identically to 15k 3.5", > > mostly > > because of the smaller diameter reducing the rotational latency. > > I think you meant smaller diameter reducing head seek time, not rotational > latency. (Rotational latency would depend on rpm's and not diameter, while > the head seek would be dependent on diameter, and not rpm's.) > > While I recognize the intuitiveness of smaller diameter --> less distance to > travel, seems to be common sense that the average head seek time should be > smaller, but I have not observed that to be the case when looking at seek > times of various sized disks (2.5" vs 3.5"). I *suspect* that the head seek > time is not so much limited by the distance it needs to travel, as it is, > microdetecting position, vibration/oscillation stabilization, and locking > onto a track. But I'm only making this guess, based on my perception that > the average seek times of 2.5" vs 3.5" disks are approximately the same.
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. 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. -- Charles Polisher _______________________________________________ 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/
