[Beowulf] small file systems
hahn at mcmaster.ca
Wed Aug 29 20:29:03 PDT 2007
> isn't have 10 slower 'datawulf' nodes better than 1 at the same speed
> (with them added up) for data access? surely the optimal speed is a
> processor that can handle the intensive IO streaming and a kernel + a bit
> of overhead for good luck.
you can never just add up speed like that - single-fast will always
have different properties from several-slow.
> another idea i have floating - with lower speed cpu's eg: 500mhz or even
> up to 1066mhz - cant you use 'normal' as you l1 cache??? surely that is
of course not, since dram is limited to ~50ns at least as currently
conceived. that would correspond with a cpu clock of around 20 MHz.
> good for data steaming eg: a 1GHz cpu with 1024MB l1 cache, a further 3GB
as a crude estimate, L1 cache takes ~6 transistors per bit, so
1G cache would correspond with 50 billion transistors, which is
much larger than current chips. such a large L2 would also not
run at 1GHz, since there is always a size-speed tradeoff.
> running at 400MHz, attached to 4 sata 2 drives?
3GB is overkill for streaming. you want your network, memory and disk
bandwidths to match, with modest buffering. if you had a 4x raid0,
you would hope to achieve around 200 MB/s, so 3GB would be an absurdly
large (15 second) buffer.
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