On 12/12/13 16:57, Pieter De Wit wrote:

On 13/12/2013 00:52, David Brown wrote:

quoted

On 12/12/13 11:27, Pieter De Wit wrote:

quoted

Hi List,

Given the recent work done with techs like CUDA etc. - has the idea been
floated to use the video card for RAID parity calculations vs the CPU ?
Bitcoin and plenty others have shown the true speed of these cards. This
might be a cheaper version of a RAID card.

Cheers,

Pieter

I am almost certain that you /could/ use a graphics card to do parity
calculations faster than a cpu core.  However, even the newly proposed
multi-parity calculations are not a big challenge for a modern cpu.  A
bigger issue is getting optimal threading so that multiple cores (or at
least threads) can be used at the same time, and this work is well under
way already.  Once that work is completed, my guess is that I/O, cache
or memory bandwidth will be the bottleneck for big raid arrays rather
than cpu power - and using graphics cards will not help there.

David


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Ah - I see - I also thought it was multi-threaded, but, tbh, I never
looked that hard into it. My question comes from the fact that I now
have access to 32x750gig (and more if needed) drives on a fiber array.
The down side is that I only have *old* CPUs driving the array. RAID5's
sync speed (15 disks) is 8meg/second. Change the array to RAID10 and the
sync speed is above 100meg/second.

When resyncing a RAID5, is the CPU running 100%? Even old CPUs should be 
able to resync faster than that. What CPU is that if I may ask?

I, naively perhaps, assumed the bottleneck to be the Intel CPU's which
sparked this idea.

What about block level hashing ? (Unless this is already done and I just
never knew it :) )

Like keeping a checksum of each RAID chunk or stripe for data 
consistency checks? RAID doesn't deal with that, it deals with 
reconstructing data in the event of a drive failure but doesn't 
guarantee data consistency. Therefore, if some bits on a drive were to 
be "flipped", the next RAID "scrub" (repair) would detect a mismatch 
between the data chunks and the parity and would simply update the 
parity from the available data (not "repairing" the corrupted data), as 
far as I know that's because there's no way for the array to know 
whether the data or the parity was written wrong or corrupted.

Regards,
Ben.

Cheers,

Pieter
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