Re: Benefits from computing physical IDE disk geometry?

Chuck Ebbert
2003-04-16T13:21:31Z

> The way you would do a good "goodness" function, I guess,
> would be to search through all requests on the device, and return
> the minimum distance from the request you are running the query
> on. Do this for both queues, and insert the request into the
> queue with the smallest delta. I don't see much else doing any
> good.

That would be perfect. And like you say in a later message, they're
in a tree so it might actually work. Then the read balance code
wouldn't need to do that calculation at all.

How hard would this be to add?

> On the other hand, if you simply have a fifo after the RAID
> scheduler, the RAID scheduler itself knows where each disk's
> head will end up simply by tracking the value of the last
> sector it has submitted to the device. It also has the advantage
> that it doesn't have "high level" scheduling stuff below it
> ie. request deadline handling, elevator scheme, etc.
>
> This gives the RAID scheduler more information, without
> taking any away from the high level scheduler AFAIKS.

But then wouldn't you have to put all that into the RAID
scheduler?

--
Chuck