On 02/10/2015 02:02 PM, Mark Hahn wrote:
?Do you know if remote swap is working well now? I remember it
working not
so good because it's a difficult problem, but I haven't tested it
lately.?
I suspect remote swap works better now, in part because systems have
been moving more towards specialized allocators. (motivated by wanting
to scale-per-core, for instance.) it was always possible to make
network-swap robust: all it takes is enough partitioning of storage
pools, so that you don't run into an allocation-swap-allocation gotcha.
is net-swap really ever a good idea? it always seems like asking for
trouble, though in principle there's no reason why net IO should be
"worse" than disk IO...
Sometimes it can be faster than disk I/O. Some SANs have massive amounts
of cache, so that data you've 'swapped to disk' might still be in the
SANs cache. I doubt this would be the case in a large cluster, but I've
seen and measured this effect first hand.
However, for HPC, I would think swapping to a network disk would
introduce some of the performance hits we're trying to avoid, like disk
latency, and add network latency on top of that.
--
Prentice
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