[Beowulf] LSI Megaraid stalls system on very high IO?
hahn at mcmaster.ca
Sat Aug 2 08:14:40 PDT 2014
> This system might have a decent amount of memory - but are the sysctl
> tunings for the dirty buffer sizes set small or something?
actually, my experience is the opposite: if sysctls permit large
accumulation of dirty buffers, a system with big memory and slow
write speeds will feel unpleasantly choppy. basically, I think
you should set vm.dirty_ratio less than the amount your storage
system can commit to disk in O(few seconds). that's the synchronous form
of writeback - I also like to make the async form more active as well.
(lower vm.dirty_background_ratio and vm.dirty_writeback_centisecs=100).
of course, this is only relevant to big-memory-slow-disk machines.
(but consider a hypothetical 1TB box with a single disk and default
settings: if it dirties 100G, the sync writeback will kick in and
saturate the disk for up to 10 minutes...)
regards, mark hahn.
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