NBUF and pstat

[Alexis Rosen]

Jim Jagielski wrote:
>Anyway, this all leads to an interesting question... certainly, as far as
>disk buffers are concerned, there is a point of diminishing returns where
>increasing the amount of buffers adds very little or even DECREASES performance
>(possibly). Does anyone have any good system tuning information for A/UX...
>25% memory for NBUF seems about right, but with large systems (32 megs) that
>still leaves a good chunk of free memory... Of course, that isn't bad since
>that means that swapping won't occur :)

Not a bad guess. When I did the MacUser A/UX review, I guessed that 10% was
a bad idea for macs with 8MB+ RAM. We did a bunch of tests and sure enough,
25% was faster each time. Problem was, the speed differences were marginal-
a few percent. It wasn't worth it for the few times when the extra 1MB of
free RAM was going to be _really_ missed, slowing down the Mac alot.

Somewhere between 15 and 20% might be a better default.

On the other hand, all these figures came from "average" tasks. Individual
habits can vary so wildly that you really have to figure out what _your_
needs are and set NBUF based on that. BTW, for the last bit of power on
all-FFS systems, set SBIFSIZE to 4096 and NBUF to NBUF/2.

Does anyone know why certain options for pstat don't seem to do anything?
I think "-p" was one...

---
Alexis Rosen
Owner/Sysadmin, PANIX Public Access Unix, NY
{cmcl2,apple}!panix!alexis