Howdy,

        I had/have problems since upgrading to a stock Redhat 7.1
2.4.2 kernel with my system{*filter*} when I try and mount a cdrom.
Now, if I turn DMA off (hdparm -d0 /dev/hdc) it no longer seems to
hang.  That'd be fine EXCEPT, despite putting the above call to
hdparm in rc.local after some period of time DMA gets turned back
on.  I've killed the autofs daemon, etc.. so I can't see quite why
or where this happens.  ANy help would be appreciated.

Regards,

        ken gibbs

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Make a shell-script calling hdparm and place it in /etc/init.d then give it a
symbolic link from the startup directory (usually rc2.d). I use this for
setting the  opposite on each boot (dma=66 and io=32bit).

-Allan

If all you want is DMA to be disabled permanently, add this to
/etc/lilo.conf:
append="ide=nodma"
and re-run lilo.  

Also, you can modify IDE parameters (on redhat 7.1) in
/etc/sysconfig/harddisks
(It's a text file that is pretty self explanatory).

If you want hdparm's stuff to "stick" you need to use some combination of
the -k1 & -K1 flags.  man hdparm for details.

--
Rex A. Dieter                   rdie...@unl.edu
Computer System Administrator   http://www.**-**.com/ ~rdieter/
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University of Nebraska Lincoln

Hi Allan,

        I did do something similar in rc.local.  The curious thing is that
while I can set -d0 switch it doesn't stay set.  For now I've resorted to
crontab and just make the call to hdparm every minute.  Not elegant but it
has the desired effect.

        Thanks for the tip though.

Regards

        Ken gibbs

--

123456789a123456789b123456789c123456789d123456789e123456789f123456789g12

     Kenneth Gibbs / VERITAS / Fred Lawrence Whipple Observatory
                  PO Box 97 / Amado, AZ / 85645-0097
  (520)-670-5719   (520)-670-5713 fax   gi...@egret.sao.arizona.edu

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That's one way of doing it, but a better way is to use RH7.1's own mechanism
for making the settings permanent.  

You'll see a file in /etc/sysconfig called "harddisks".  Copy that file to
/etc/sysconfig/harddisk<dev>  where dev is the device name of your CDROM.
For example, if your CDROM is /dev/hdc, make a copy of the file
to /etc/sysconfig/harddiskhdc

then edit that specific file and uncomment the DMA line but make sure it's set
to 0 not 1.  When you reboot use hdparm to check that the device does not have
DMA enabled.

RH7.1's stock kernel selected "Use PCI DMA by default" which makes all devices
use DMA by default.  I recompile my kernel to NOT use this feature and then enable
it using the harddisk file...

Dave

There's a good chance that it gets disabled for a reason - check the output
of the 'dmesg' command.

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if you want the IDE settings to stay the way you configured them with
hdparm, use this:
hdparm -k1 /dev/<harddisk>

i.e. hdparm -c1 -d1 -m8 -k1 /dev/hda will set hda in 32 bit mode with
DMA on and multiple sector count at 8. the -k1 option will results in
restoring these settings upon a IDE reset.

hope this helps

roger