Subject: Re: a thought about FFS parameters & disk performance
To: None <current-users@NetBSD.ORG>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: current-users
Date: 05/12/1997 11:27:53
> The Fast Filesystem has lots of knobs for tuning performance.  I
> don't fully understand the effect of turning any one of those knobs
> in one direction or the other.  How many people really do?

Maybe as many as a dozen?  (My guess.)

> In one sense, disk technology has not changed much since Kirk did the
> work (we still have platters that spin with heads that seek),
> however, some things have changed (e.g. Fast SCSI, Fast & Wide SCSI,
> Ultra SCSI, IDE, EIDE, plus disks that spin at 4500, 5400, 7200, and
> higher RPM),

None of those really invalidate much of the FFS stuff.  What does break
it is things like ZBR (where sectors/track varies depending on cylinder
number), on-disk caches, automatic bad sector replacement (though IIRC
the FFS layout code never made any attempt to deal with the
implications of bad sector forwarding), bit densities high enough that
DMA can't keep up with the disk....

Personally, I'd much rather find that damn bug in the rotational layout
code first.  I really want fsresize working.

					der Mouse

		     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B