On Thu, 2006-11-23 at 18:21 -0700, Peter Braam wrote:
> I'd just like to take one step back here for the reading problem - let's
> keep it simple.
>
> When we worked with DDN 8500 controllers we established that with
> something like 10 reading threads reading 1MB chunks randomly from OSTs
> we achieved the full bandwidth of the array.
>
> Read-ahead probably only damages things at this point (but is very
> important for reading smaller files).
>
> There are many users of the 9500 SATA arrays now, and it surprises me
> that we don't have the OST survey graphs for these arrays. I believe
> that someone from our staff is at work with Sandia to get one done.
> This should show us the parameters to get full bandwidth at least when
> the application reads at least X MB, where X is hopefully still 1 (if
> not we have a nasty networking problem on our hands).
>
> I would say that "playing" with the parameters (DDN settings, Lustre
> read ahead etc) is almost certain to make things worse in these use
> cases, and be highly confusing. Perhaps we should disable at least the
> Lustre read-ahead stuff when we have the minimum sizes to reach full
> bandwidth.
I believe we already know what to do to accomplish what you suggest.
However, could you take the time to be explicit? Better that we know
than believe...
--Lee
>
> - peter -
>
>
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