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============================================
INTEL ISA library Erasure Coding plugin
============================================
Build Requirements
==================
Plug-in build compiles the included sources of ISA-L v2.10 and links them into the plugin. ISA-L implementation is portable and probes CPU features during runtime. Note that the names of the assembler source files have been renamed from *.asm to *.asm.s to be compatible with Automake.
Run-time Requirements
=====================
None
Plug-in Configuration
=====================
Used parameters are:
k : number of data chunks
m : number of coding chunks
technique : cauchy, reed_sol_van
The plug-in exports only two encoding technique (cauchy, reed_sol_van) using either a Vandermonde matrix or a Cauchy matrix for coding.
By default a Vandermonde matrix is used. Be aware that sometimes the generated Vandermonde matrix is not always invertible and not fully MDS.
Therefore the accepted parameter space has limited to maximum (21,4) and (32,3) for Vandermonde matrices.
Run the Test suite
==================
cd ceph/src
make unittest_erasure_code_isa
./unittest_erasure_code_isa --gtest_filter=*.* --log-to-stderr=true --debug-ods=20
Run the CEPH erasure code benchmark
===================================
cd ceph/src
make ceph_erasure_code_benchmark
# consult ./ceph_erasure_code_benchmark -h for help
# encode performance
./ceph_erasure_code_benchmark -p isa -P k=8 -P m=3 -S 1048576 -i 1000
# decode performance one lost
./ceph_erasure_code_benchmark -e 1 -w decode -p isa -P k=8 -P m=3 -S 1048576 -i 1000
# decode performance two lost
./ceph_erasure_code_benchmark -e 2 -w decode -p isa -P k=8 -P m=3 -S 1048576 -i 1000
# decode performance three lost
./ceph_erasure_code_benchmark -e 3 -w decode -p isa -P k=8 -P m=3 -S 1048576 -i 1000
Developer Notes
===============
The plugin provides optimal performance for 32-byte aligned buffer start address and
k*32 byte aligned buffer length. The encoding tables are computed only once when the EC
object is created. Decoding Tables have to be computed for each decoding since the available
data/coding sources may change between calls.
Decoding tables are cached in an LRU cache which is sufficiently large up to (12,4).
For larger configurations the cache might expire the 'oldest' tables and decoding might
slow down. The plug-in uses an optimization to use a pure region XOR to decode single disk
failures if the erased chunk is within the first (k+1) chunks.
The unittest probes all possible failure scenarios for (12,4) Vandermonde and Cauchy matrices.
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