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diff --git a/doc/rados/operations/erasure-code-jerasure.rst b/doc/rados/operations/erasure-code-jerasure.rst
index 8a0207748ae..c3717750754 100644
--- a/doc/rados/operations/erasure-code-jerasure.rst
+++ b/doc/rados/operations/erasure-code-jerasure.rst
@@ -60,6 +60,24 @@ Where:
*blaum_roth*, *liber8tion* are *RAID6* equivalents in
the sense that they can only be configured with *m=2*.
+ .. note:: When using ``blaum_roth`` coding, the default
+ word size of ``w=7`` is suboptimal because ``blaum_roth``
+ works best when ``w+1`` is prime. When creating a new
+ erasure-code profile with ``technique=blaum_roth``,
+ set ``w`` to a number that is one integer less than a prime
+ number (for example, ``6``). See `Loic Dachary's
+ commit f51d21b to ceph/ceph <https://github.com/ceph/ceph/commit/f51d21b53d26d4f27c950cb1ba3f989e713ab325>`_ for information about
+ why this default cannot be changed easily in the
+ source code, and see `the second bullet point on
+ page 29 of Plank and Greenan's "Jerasure: A Library
+ in C Facilitating Erasure Coding for Storage
+ Applications" <https://github.com/ceph/jerasure/blob/master/Manual.pdf>`_ for an unequivocal statement of the restriction that applies
+ to ``w`` when using Blaum-Roth coding.
+ (Information about the proper value of ``w`` when
+ using ``blaum_roth`` coding was provided to the
+ Ceph upstream in September of 2024 by Benjamin
+ Mare.)
+
:Type: String
:Required: No.
:Default: reed_sol_van