Date: Fri, 1 Feb 2013 16:31:30 -0000 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Steven Hartland" <killing@multiplay.co.uk>, "Wojciech Puchar" <wojtek@wojtek.tensor.gdynia.pl>, <freebsd-hackers@freebsd.org> Subject: Re: HDD write cache Message-ID: <72C01AB30B93443C8C6F1183A04BBE30@multiplay.co.uk> References: <alpine.BSF.2.00.1302011524480.43260@wojtek.tensor.gdynia.pl> <DF4C0697C59747BEBE5DF564E0B934EB@multiplay.co.uk>
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Investigating a bit more a device reset will also trigger the
change so after changing the value you can use camcontrol reset
to trigger the change to apply using e.g.
camcontrol reset 0:0:0
While this is stated in the man for ada its not obvious that
changing the sysctl without a reset won't work, so you might
want to raise a PR about it.
Regards
Steve
----- Original Message -----
From: "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"
>
>> 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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