Thanks for the follow-up.

Lets start with normal erasure coding plugin. Here we have k data node and
m parity nodes.
For RDP or RAID-DP or MSR/MBR kind of erasure code the codeword is two
dimensional array.

FOr example, in case of RDP Erasure code the cored is kx(k+m) array. The
codeword has k rows and n columns (i.e. k + m)
The first k columns represents the systematic data and the last m columns
represents the parity data.
Here the object to be divided into kX(k+m) symbols. The RDP Erasure code
has one row parity and rests are diagonal parity.
Pl. make google image for RDP Erasure Code diagram.

I'm I making sense...

Thanks,
Syed

On Mon, Feb 1, 2016 at 9:03 PM, Syed Hussain <syed...@gmail.com> wrote:

> Hi,
>
> I've been working to develop a CEPH EC plgin for array type erasure code,
> for example
> RAID-DP (i.e RDP). Later I realized that I can't continue with (k+m)
> format in CEPH as
> like normal RS code if I want to save disk IO (or Read data).  Since I
> need to ready the individual symbols from each device rather that k
> symbols. One "chunk" from OSD will contain k-symbols
> in contiguous form. The same thing will be an issue for MSR(Minimum
> Storage Regeneration) Erasure code plugin.
>
> As a solution I thought to consider k*k data chunk and k*m coding chunk
> and use LRC kind of
> layering to pass the info (in plugin) which is data chunk and coding chunk.
> However, I've doubt if the decoding API will supply me the correct info on
> lost chunks to get the info on lost erasure coding nodes.
>
> Does anybody have good solution to this issue using CRUSH map?
> Could Pl. suggest any pointer or link that explain the above issue?
>
> Thanks,
> Syed Abid Hussain
>
>
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