HDD write cache

[Steven Hartland]

Looking at the cam ata code I can't see how those values would do
anything after booting.

I suspect they should be loader only tunables with the current code
and cant be changed on the fly for a disk that's already been
registered.

Try setting the values in /boot/loader.conf if you haven't already?

You can check the actual status of the disk itself using:-
camcontrol identify ada0

    Regards
    Steve

----- Original Message ----- 
From: "Wojciech Puchar" <wojtek at wojtek.tensor.gdynia.pl>
To: <freebsd-hackers at freebsd.org>
Sent: Friday, February 01, 2013 2:26 PM
Subject: HDD write cache


> after reading quite recent topics about disabling/enabling write cache, i 
> tried to test in on desktop 3.5" drive
> 
> kern.cam.ada.write_cache: 1
> kern.cam.ada.read_ahead: 1
> kern.cam.ada.0.read_ahead: -1
> kern.cam.ada.0.write_cache: -1
> 
> i tried writing 1 or 0 to kern.cam.ada.0.write_cache, and there were 
> exactly no differences at all, and disk seems to do always write caching.
> 
> Does that drive lie and ignore commands or i do it wrong?
> 
> this is my disk.
> 
> ada0 at ahcich0 bus 0 scbus0 target 0 lun 0
> ada0: <SAMSUNG HD501LJ CR100-10> ATA-8 SATA 2.x device
> ada0: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes)
> ada0: Command Queueing enabled
> ada0: 476940MB (976773168 512 byte sectors: 16H 63S/T 16383C)
> 
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