[Disksim-users] Seek time calculation

[John Bucy]

On Fri, 2005-07-15 at 16:24 -0400, Ozlem Akpinar wrote:
> Hi, 
> For my disk, I am using hpl seek time function. I set up the requests
> so that only the second part of the equation is valid. However, Avg
> seek distance value is not matching the avg. seek time value reported
> in the output file. (I am supposed to get a different avg seek time
> value if I plug the avg seek distance value into the hpl seek time
> equation)

1.  The hpl equation is *old*.  All modern disks have a seek curve too
tricky to be accurately modeled by it; we use a piecewise/extracted
curve ("full seek curve") instead.

2.  It may be hard to make a sensible comparision between the average
seek time of the disk "on paper" and under a real workload.  If your
workload is uniformly random across the entire LBN space, I'd think it
might match up but under any other circumstances, the distribution of
the trace and effects of the cache will change it.



john