Re: Benefits from computing physical IDE disk geometry?

Chuck Ebbert
2003-04-13T17:56:34Z

Nick Piggin wrote:

>>
>> Any good SCSI drive knows the physical geometry of the disk and can
>> therefore optimally schedule reads and writes. Although necessary features,
>> like read queueing, are also available in the current SATA spec, I'm not
>> sure most drives will implement it, at least not very well.
>>
> The "continuous" nature of drive addressing means that the kernel
> can do a fine job seek-wise. Due to write caches and read track
> buffers, rotational scheduling (which could be done if we knew
> geometry) would provide too little gain for the complexity. I would
> say that for most workloads you wouldn't see any difference. (IMO)

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.

--
Chuck