Shared Memory

[Peter L. Peres]

On Tue, 1 Feb 2005, Lennart Sorensen wrote:

> On Tue, Feb 01, 2005 at 11:43:39AM +0200, Peter L. Peres wrote:
>> I thought ncq was beneficial on scsi because several devices share the
>> bus. On sata there is only one per bus. How would they benefit from ncq
>> ?
>
> No the idea is to issue multiple commands to each device in a queue and
> letting the device schedule which order to serve them in based on where
> it's head is and which order will get all the data the fastest.  Old
> scsi disks might only have had an 8 command queue, while many newer
> drives have 256 command queues.

Thanks,

Is this not what is known as 'multi session' access ? I am familiar with 
the concept. I am also under the impression that the OS does some 
command sheduling based on its knowledge of the disk geometry (like 
cylinder striping and grouping) and the drive's own ideas about this 
optimisation may collide with it. No ?

thank you,
Peter

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