More Adaptec 29320 + Seagate ST336607LW woes

[Nate Lawson]

On Sat, 6 Dec 2003, Don Lewis wrote:
> On  6 Dec, ian j hart wrote:
> > I thought tagged queuing needed WCE.
>
> One place where folks have noticed a performance difference between WCE
> on and WCE off is when using newfs after we got rid of the buffered
> block devices and forced newfs to use the raw character device.  Newfs
> only issues one write() at a time and waits for the status before
> issuing another write().  If WCE is on, the writes only have to hit the
> drive cache before the drive returns a status that gets returned to
> userland, but if WCE is off the data has to hit the platter before the
> status is returned, which slows down newfs quite considerably.  Tagged
> queuing doesn't make any difference in this case because the drive will
> only see at most only one command at a time.

Great explanation.  We should probably add write clustering to newfs at
some point.

-Nate