Re: Comments on Ceph distributed parity implementation

[Loic Dachary <loic@dachary.org>]

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Hi Benoît,

From the ( naïve ) point of view of engineering, performances are important. The recent works of James Plank ( cc'ed ) greatly improved them
 and I'm looking forward to the next version of jerasure ( http://web.eecs.utk.edu/~plank/plank/papers/CS-08-627.html ). Rozofs Mojette Transform implementation ( https://github.com/rozofs/rozofs/blob/master/rozofs/common/transform.h & https://github.com/rozofs/rozofs/blob/master/rozofs/common/transform.cc ) does not seem to make use of SIMD. Is it because the performances are good enough to not require them ?

Cheers

On 06/16/2013 09:51 PM, Benoît Parrein wrote:
> Paul Von-Stamwitz <PVonStamwitz <at> us.fujitsu.com> writes:
> 
> Hi Paul, 
> 
>>
>> Loic, I know nothing about Mojette Transforms. From what little I gleaned, 
> it might be good for repair
>> (needing only a subset of chunks within a range to recalculate a missing 
> chunk) but I'm worried about the
>> storage efficiency. RozoFS claims 1.5x. I'd like to do better than that.
>>
>> All the best,
>> Paul
>>
> 
> If you want to do better than that you will probably lose in availability. 
> 1.5x give the same availability than 3 replicats and that for any kind of 
> erasure coding.
> FYI, Mojette transform has no constraint in terms of Galois fields. It is the 
> big advantage to use discrete geometry rather than algebra.
> 
> best regards,
> bp
> 
> 
> 
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-- 
Loïc Dachary, Artisan Logiciel Libre
All that is necessary for the triumph of evil is that good people do nothing.


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