Re: Problem in IDE Disks cache handling in kernel 2.4.XX

[Andre Hedrick]

Oh, just let the darn thing barf a 0x51/0x04 is fine with me!
Just an abort/unsupported command.

Cheers,

On 10 Jan 2003, Alan Cox wrote:

> On Fri, 2003-01-10 at 11:14, Andre Hedrick wrote:
> > The drive does random and automatic flush caches, if an error happens it
> > does not report. *sigh*  When APM hits it with a flush and pray the error
> > is from this flush, but it does not matter ... the kernel does not have
> > the paths to deal this issue ... so bye bye data!  Now it if the current
> > flush is not the owner of the error OMFG is suggested.
> 
> For that matter the BIOS tends to issue the flush, in fact APM is
> supposed to be transparent so the BIOS is required to handle it and
> since a critical shutdown from the APM PM might not even hit the OS
> it has to. Of course pigs also fly 8)
> 
> > > > I had a look at patch 2.4.21pre3 and the code looks the same.
> > > > 
> > > > And by the way how are powered off the IDE drives ?
> > > > Because a FLUSH CACHE or STANDY or SLEEP is MANDATORY before powering off the 
> > > > drive with cache enabled or you will enjoy lost data
> > > 
> > > IDE disagrees with itself over this but when we get a controlled power
> > > off we do this. The same ATA5/ATA6 problem may well be present there
> > > too. I will review both
> > 
> > Not true, the firmware knows to commit the data to platter.
> > If it was true you would be screaming long ago.
> 
> IDE disagrees with itself because it is meant to work compatibly but if
> you run it compatibly you lose data on poweroff.
> 
> > 
> > > Any specific opinion Andre ?
> > 
> > A dirty trick used to date is to pop the STANDY or SLEEP, and depend on
> > the drive to deal with the double dirty flush error.  If the FLUSH CACHE
> > was not valid, the drive would spin back up from STANDY, but not from
> > SLEEP, this could be a problem.  However SLEEP issued by the driver only
> > happens at shutdown unless it has been changed.  In the shutdown process,
> > each partition unmount was flushed and also once extra when the usage
> > count was set to zero.  Worst case was 2 flush min.
> > 
> 
> The original question however is whether we are skipping issuing the flush
> and sleep on ATA3-5 devices when we should not, because the test is over
> strong.
> 
> It seems weakening the test is the best option, it fixes ATA-5 and any device
> told to sleep, standby or flush that doesn't know the command is just going
> to go "Huh ?" and we'll get a nice easy to handle error.
> 
> Alan
> 
> 

Andre Hedrick
LAD Storage Consulting Group