On 07/17/2009 11:40 AM, H. Peter Anvin wrote:
Ric Wheeler wrote:
I have seen the papers; I'm not sure it really makes that much
difference. One of the things that bugs me about these papers is that he
compares to *his* implementation of my optimizations, but not to my
code. In real life implementations, on commodity hardware, we're limited
by memory and disk performance, not by CPU utilization.
Fair enough - I thought that his coverage of the other open source
friendly encodings beyond RAID6 was actually quite interesting.
If you have specifics that you found unconvincing in his work, I am
pretty sure that he would be delighted to hear from you first hand.
James seemed to me to be very reasonable and very much a pro-Linux
academic, so I would love to be able to get him and his grad students
aligned in a useful way for us :-)
The main flaw, as I said, is in the phrase "as implemented by the
Jerasure library". He's comparing his own implementations of various
algorithms, not optimized implementations.
The bottom line is pretty much this: the cost of changing the encoding
would appear to outweigh the benefit. I'm not trying to claim the Linux
RAID-6 implementation is optimal, but it is simple and appears to be
fast enough that the math isn't the bottleneck.
-hpa
Cost? Thank about how to get free grad student hours testing out things that you
might or might not want to leverage on down the road :-)
ric
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