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SubjectRe: Fix disk statistics reporting on each disk (logical)
On Wed, Aug 30 2000, Nikolaiev, Mike wrote:
> OK... I cannot resist...
>
> Working with large database systems,
> (700MHz 32P, 32GB ram, 500-18GB 15K drives)(Well I think it is big)
> We often configure many logical drives on a disk array controller.
> Each of these are represented under Linux as a minor dev number.
> We may have 50-70 logical drives on the system, each with 14 to 56 drives
> each.
>
> In order to balance the database load across all the spindles evenly, we
> monitor # of reads/sec; # of writes/sec; min,max, and avg latency (service
> time);
> and avg # of outstanding I/O's (queue length) on a per logical drive basis.
>
> If we find some drives overloaded and others lightly loaded we balance the
> data.
>
> Will we have the capabilities stated above?

When the sar patch gets integrated, then yes. The basic accounting
that is done now doesn't give you enough information to determine
service time and queue length, etc.

> If not, is it very difficult to put these in the kernel at this point?

No, there are already patches out there to do it.

> I would envision us supporting systems of this size on Linux next year on
> the 2.4 kernel
> and we really need this kind of data to tune the system...

I would like that too, and cleaning up the statistics stuff would be a
good time to wrap the sar patch in. It's clean and fairly non-intrusive...

--
* Jens Axboe <axboe@suse.de>
* SuSE Labs
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