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<font size="+1"><tt>Hi CLUEbies,<br>
<br>
For various very important reasons we have to run our Linux systems
with CentOS 5.x with all IDE drives in UDMA2 (or slower) mode. Of
course the 2.6 kernel IDE device driver, the chipset on our
motherboard, and the drives, all support UDMA5 or UDMA6 and
autonegotiate the fastest speed they support when the driver
initializes the drive.<br>
<br>
When we try to use hdparm to change it back to UDMA2 (hdparm -d 1 -X
udma2 /dev/hdX) we occasionally get errors. We think there are some
timing issues in hdparm and possibly the kernel, and probably the IDE
drive firmware too. We have a dizzying variety of
chipsets/motherboards and hard drives and depending on the combination
of those (and whether or not we have a 40 pin or 80 pin IDE cable) we
occasionally get errors like this:<br>
<br>
hda: set_drive_speed_status: status=0x58 { DriveReady SeekComplete
DataRequest }<br>
ide: failed opcode was: unknown<br>
ide0: Drive 0 didn't accept speed setting. Oh, well.<br>
hda: CHECK for good STATUS<br>
<br>
AND THEN DMA IS DISABLED WHICH IS REALLY BAD FOR OUR SYSTEMS. Please
don't suggest that the drives are bad because we have exhaustive drive
tests and all drives which fail this way pass all the tests.<br>
<br>
We also tried booting the kernel with ide=nodma and then one of the
first init scripts turns on UDMA2. This makes the above error happen a
lot less often (maybe 95% less) but it still happens repeatably from
time to time.<br>
<br>
I think that trying to set the DMA mode after initialization is maybe
not a good idea. If we could make the 2.6.18 IDE driver start up in
UDMA2 mode instead of the default fastest mode that might sidestep the
problem altogether. Does anyone in CLUEland know what is the fastest
way to do this? By the way the IDE driver in the CentOS 5.x kernel
(2.6.18) is not a module. My googling has not turned up anything and
there is no kernel command line option for the IDE driver that does
this.<br>
<br>
Thanks,<br>
Jim<br>
</tt></font>
<pre class="moz-signature" cols="72">--
Jim Ockers, P.Eng. (<a class="moz-txt-link-abbreviated" href="mailto:ockers@ockers.net">ockers@ockers.net</a>)
Contact info: <a class="moz-txt-link-freetext" href="http://www.ockers.ca/pason.html">http://www.ockers.ca/pason.html</a>
</pre>
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