doc/rados: clarify default EC pool from simplest

Distinguish between the default erasure-coded pool (k=2 m=2) and the
simplest erasure-coded pool (k=2 m=1).

Signed-off-by: Zac Dover <zac.dover@gmail.com>
(cherry picked from commit 63c27ab8e746127b89120d4c47b427d13433758c)

diff --git a/doc/rados/operations/erasure-code.rst b/doc/rados/operations/erasure-code.rst
index ca267594135918413e69e8f00ab3dee522236cfd..1dea23c35168da1bd129a6cb1baece14356928ff 100644 (file)
--- a/doc/rados/operations/erasure-code.rst
+++ b/doc/rados/operations/erasure-code.rst
@@ -67,6 +67,16 @@ profile can be displayed with this command:
    crush-failure-domain=host
    technique=reed_sol_van
 
+.. note::
+   The default erasure-coded pool, the profile of which is displayed here, is
+   not the same as the simplest erasure-coded pool. 
+   
+   The default erasure-coded pool has two data chunks (k) and two coding chunks
+   (m). The profile of the default erasure-coded pool is "k=2 m=2".
+
+   The simplest erasure-coded pool has two data chunks (k) and one coding chunk
+   (m). The profile of the simplest erasure-coded pool is "k=2 m=1".
+
 Choosing the right profile is important because the profile cannot be modified
 after the pool is created. If you find that you need an erasure-coded pool with
 a profile different than the one you have created, you must create a new pool