Bug#606968: DMA: Out of SW-IOMMU space with Xen kernel during heavy I/O

[Rik Theys <Rik.Theys@esat.kuleuven.be>]

Ben,

On Tue, 14 Dec 2010, Ben Hutchings wrote:
> mpt2sas was not using the correct test for whether DMA mapping
> succeeded, so it tried to continue after the DMA mapping failure.  This
> has been fixed in a later version and I will apply the fix to Debian's
> branch of 2.6.32.

Thanks!

> However, even if this type of error is handled properly, I think it will
> result in the filesystem being switched to read-only mode, and you will
> then have to reboot.  Using RAID may mitigate this.

What do you mean when you say that RAID may mitigate this? This system _has_
a RAID controller and the disk is in a RAID1. Why would the filesystem switch
to read-only mode? Is it because the RAID is too slow? If the RAID is too slow, 
this should just give a high iowait, but not make the file system read-only?

Is it normal that I couldn't reproduce this with the non-xen kernel? Or can that
be caused by the fact that the stock kernel had access to all the memory (72GB),
but the dom0 kernel was limited to 2GB?

Regards,

Rik