[Beowulf] LSI Megaraid stalls system on very high IO?

[mathog]

On 31-Jul-2014 12:00, beowulf-request at beowulf.org wrote:
> 
> Switch them to deadline or noop.
> 
> echo deadline > /sys/block/sda/queue/scheduler
> 
> rinse and repeat for other devices.

That may fix the problem but I am still curious about exactly what 
happened during the terminal stalls.   Using the current cfq scheduler 
what is going on in the system that is keeping those terminal processes 
from getting any CPU time?  These wouldn't respond to a carriage return 
or an X11 redraw event, and that interaction should have been entirely 
within bash and other programs already in memory, so there should not be 
any contention for disk IO there.

Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech