On Sat, 1 Dec 2007, Tomasz Ostrowski wrote:
> You can also use "hdparm -I" to check this - look for a "Write
> caching" in "Commands/features" section. If it has a "*" in front
> then it is enabled and dangerous.
Right; using -I works with most Linux hdparm versions:
# hdparm -V
hdparm v6.6
# hdparm -I /dev/hda | grep "Write cache"
* Write cache
# hdparm -W 0 /dev/hda
/dev/hda:
setting drive write-caching to 0 (off)
# hdparm -I /dev/hda | grep "Write cache"
Write cache
While being able to check the state with -W only works in very recent
ones.
The best way to make this change permanent varies depending on your Linux
distribution.
Also: nowadays many SATA disks appear as SCSI devices like /dev/sda. In
some cases I believe you can use a recent hdparm on them anyway, in others
I've had to use sdparm instead. Several of the examples at
http://sg.torque.net/sg/sdparm.html show how to manipulate the Write Cache
Enabled (WCE) status similarly to the above on SCSI devices.
> I don't know how to check it on BSD.
In FreeBSD I believe you use atacontrol to check the settings, and you can
make the changes permanent by fiddling with the /boot/device.hints file.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD