On Tue, 2010-12-14 at 13:24 +0100, Rik Theys wrote: > 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? 'mitigate' means to make a problem less bad. > 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? The DMA mapping failure will be treated as an I/O error. Most filesystems do not attempt to retry after an error. This has nothing to do with the speed of the disk. Since you use RAID, the failure may only put a single disk in degraded state, which will then be recoverable in the usual way. The error would be hidden from the filesystem. > 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? That may be part of the problem, but I think this is a software limitation in Xen. Ben. -- Ben Hutchings Once a job is fouled up, anything done to improve it makes it worse.
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