Re: Benefits from computing physical IDE disk geometry?

Nick Piggin
2003-04-14T04:18:50Z

Alan Cox wrote:

>On Sul, 2003-04-13 at 19:03, Chuck Ebbert wrote:
>
>> OTOH you can come up with scenarios like, say, a DBMS doing 16K page
>>aligned IO to raw devices where you might see big gains from making sure
>>those 16K chunks didn't cross a physical cylinder boundary.
>>
>
>You couldn't even tell where such boundaries exist, or what the real
>block size of the underlying media is. Cyliners are all different sizes.
>
Yes this is getting very difficult as Alan said. Its also something
that we can't do in kernel - the block io scheduler can only choose
from what it is given. I wouldn't be surprised if big databases did
try using some sorts of disk mapping systems to help optimise
their IO however.