problem with a cobalt RaQ550 system and DMA (Serverworks OSB4 in impossible state)

[Olivier Bornet <Olivier.Bornet@puck.ch>]

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Hello,

I'm trying to install Debian on 4 RaQ550 with each 2 80GB disks. All
seems OK with 3 of RaQ, but with one, it crash when I put the two disks
in a RAID1 meta device. In fact, it as crash at about 6% before the 70GB
partition is fully synchronized.

The error message is:

===================================================================
Serverworks OSB4 in impossible state.
Disable UDMA or if you are using Seagate then try switching disk types
on this controller. Please report this event to osb4-bug@ide.cabal.tm
OSB4: continuing might cause disk corruption. 
===================================================================

I have also send the same email as this one to osb4-bug@ide.cabal.tm.

After some search, it seems I must enable MWDMA for my disks. (ref:
http://www.cs.helsinki.fi/linux/linux-kernel/2002-33/0836.html )

Here is the configuration : 2 IDE 80GB disks, one on hda, one on hdc.
The kernel is the stock 2.4.20, with cobalt patches. The cobalt patches
don't modify the drivers/ide/serverworks.c.

IDE part of lspci -v:

00:0f.1 IDE interface: ServerWorks CSB5 IDE Controller (rev 92) (prog-if 8f [Master SecP SecO PriP PriO])
        Subsystem: Sun Microsystems Computer Corp.: Unknown device c000
        Flags: bus master, medium devsel, latency 64
        I/O ports at fcd8 [size=8]
        I/O ports at fcd4 [size=4]
        I/O ports at fcc8 [size=8]
        I/O ports at fcc4 [size=4]
        I/O ports at fcb0 [size=16]
        I/O ports at fcac [size=4]

/proc/ide/hda and /proc/ide/hdc say it's a ST380021A. (I have no
physical access to the system now...)

I have try to set the DMA of the disks with:
    hdparm -X66 -d 1 /dev/hda
    hdparm -X66 -d 1 /dev/hdc
but this has cause a direct hangup (with the same message "Serverworks
OSB4 in impossible state...."). Maybe I don't use correctly hdparm, as
this is my first attempt with it.

At this time, I have disabled the dma with:
    hdparm -d 0 /dev/hda
    hdparm -d 0 /dev/hdc
and the sync in in the way (but say we need about 6 hours to finish,
comparing to the unmodifed test giving about 1 hour).

So my questions are :

- what can I do ?
- may this problem come also with the others RaQ we have (as far as I
  know, they are the same, and they are ordered at the same time)
- is the system safe without dma ?

Thanks in advance for any help, or any pointer to a solution. (Of
course, I can apply a patch to the kernel if this may correct the
problem).

		Olivier
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