NCQ Re: Disk write caching, hw.ata.wc and atacontrol disagree)

[Dieter]

>> So hw.ata.wc thinks that the disk write cache is off,
>> but atacontrol cap thinks the disk write cache is on?

> I remember this is working but there was a reporting problem
> in atacontrol.

Looks like "atacontrol cap" reports the state of the disk *before*
hw.ata.wc took effect.

It would be less confusing if "atacontrol cap" reported the state
of the disk at the time atacontrol is run.

> You should easily be able to tell whether it is on or off by the
> write performance.  It should plummet by a factor of 4 or so.

I'm seeing only ~10% of the performance I get with the write cache on.

Which leads to:

Feature                      Support  Enable    Value           Vendor
Native Command Queuing (NCQ)   yes       -      31/0x1F

Where is the knob to turn on NCQ?  My controller and disks claim to support
it, but grepping the 6.0 man pages finds nothing.