Re: Pluggable Disk Schedulers in GEOM

Siterer Poul-Henning Kamp <phk_at_phk.freebsd.dk>:
> In message <20070105015800.s3rqdzgm8k8owk4s_at_webmail.ntnu.no>,   
> lulf_at_stud.ntnu.no
>  writes:
>
>> I was wondering if someone have started on the pluggable
>> disk-scheduler project
>> on the "new ideas"-page yet.
>>
>> I was thinking on how one could implement this in GEOM by [...]
>
*snip*
>
> Here are some ideas:
>
> Remove disksorting and see if if and how big a difference
> it makes today.  Test both SCSI, ATA and USB media, and
> test both low-level benchmarks and "real-world" workloads.
>
> Change disksorting to reverse unidirectional elevator
> and bidirectional elevator and see if it makes a difference.
> (Modern disks store blocks in reverse sector order on
> the disk, discover and explain why)
>
> Capture an I/O trace from a suitably sensible realworld
> system, including the detailed timestamps of issuance
> and completion of the requests.  Treat results statistically
> and try to determine a formula for predicting how long
> a given request is going to take for the disk.
>
> It's not that I think that all your ideas are bad, I am just
> not sure that the (traditional) view of the hardware they
> are based on, is still relevant, and I think your time would
> be much better spent addressing that question.
>
I understand, and I clearly see the point about new hardware being  
more intelligent in these matters.

However, I will look into this a bit more just out of curiosity, and  
do some actual test on how this can affect performance in the  
scenarios you describe. And thanks for the tips!

-- 
Ulf Lilleengen