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erasure-code: restore jerasure BlaumRoth default w

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Changing from W=7 to W=6 by default for the BlaumRoth technique is
correct but introduces a regression. The content that was encoded with
the previous version cannot be read again. Although the prime(w+1)
constraint was not obeyed by W=7, the encoded content was useable and
should keep being readable.

The W=7 remains the default for backward compatibility and an exception
to the prime(w+1) check.

http://tracker.ceph.com/issues/9572 Fixes: #9572

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
This commit is contained in:
Loic Dachary 2014-09-23 11:11:59 +02:00
parent 86bdd044e4
commit f51d21b53d
2 changed files with 4 additions and 1 deletions
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4
src/erasure-code/jerasure/ErasureCodeJerasure.cc
View File

@ -454,6 +454,10 @@ void ErasureCodeJerasureLiberation::prepare()
//
bool ErasureCodeJerasureBlaumRoth::check_w(ostream *ss) const
{
// back in Firefly, w = 7 was the default and produced useable
// chunks. Tolerate this value for backward compatibility.
if (w == 7)
return true;
if (w <= 2 || !is_prime(w+1)) {
*ss << "w=" << w << " must be greater than two and "
<< "w+1 must be prime" << std::endl;

1
src/erasure-code/jerasure/ErasureCodeJerasure.h
View File

@ -236,7 +236,6 @@ public:
ErasureCodeJerasureBlaumRoth() :
ErasureCodeJerasureLiberation("blaum_roth")
{
DEFAULT_W = 6;
}
virtual bool check_w(ostream *ss) const;