vinum performance

[Greg 'groggy' Lehey]

On Sunday, 30 March 2003 at 18:10:07 +0200, Dag-Erling Smrgrav wrote:
> Lukas Ertl <l.ertl at univie.ac.at> writes:
>> I'm currently testing with prime stripe sizes, but it doesn't seem to
>> help. I additionally added "options AHC_ALLOW_MEMIO" to the kernel, and it
>> has raised write performance in the single-disk case (although I'm not
>> happy with that one either; I expected a disk on a U160 controller to pump
>> out more than ~65MB/s).
>
> Does the data sheet for your disk indicate that it can in fact write
> much faster than that?  The speed at which data is actually written
> to the media is much lower than the bus speed - the bus speed *has*
> to be higher to accomodate multiple devices.

You're touching on one of the real issues here.  For optimum
transfers, a plex needs large stripes.  If you're only doing one
transfer at a time (like bonnie does), you'll just pick on individual
disks alternately, so the performance can't be much better than a
single disk.  Do a large number of simultaneous transfers and it will
be a different story.

Greg
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