Re: sequential disk read speed

On Aug 24, 12:39 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>
> If you have a 100GB database and you put it on single
> 100GB disk drive, your best average seek time is the average seek time of
> the disk drive, but if you put the database on four 100GB disk drives, the
> the best average seek time will only be a fraction of the seek time of the
> single disk. Suppose that the full-stroke seek time on the 100GB disk is
> 7ms and the track-to-track seek time is 1ms. Well, with four disks, instead
> of an average 4ms seek time, the individual seek time of each disk is
> reduced to roughly 2.5ms

Is this because less of the disk is actually being used so on a given platter the head doesn't have such a large range of tracks to move over?

> , and since there are four disks, the average seek
> time for the disk subsystem is reduced to a quarter of that or roughly
> .625ms.

In order for the effective seek time to be reduced to a quarter the seeking must be independent. To achieve that I think the striping would need to be very coarse (eg 512kb or 1Mb). Received on Thu Aug 28 2008 - 03:46:50 CEST