diff --git a/en_US.ISO8859-1/books/handbook/config/chapter.sgml b/en_US.ISO8859-1/books/handbook/config/chapter.sgml
index f139ad3166..aaf4671a26 100644
--- a/en_US.ISO8859-1/books/handbook/config/chapter.sgml
+++ b/en_US.ISO8859-1/books/handbook/config/chapter.sgml
@@ -1678,12 +1678,25 @@ kern.maxfiles: 2088 -> 5000</screen>
         will require you to use the <option>NMBCLUSTERS</option> kernel
         &man.config.8; option.</para>
 
-      <para>Under <emphasis>extreme</emphasis> circumstances, you may need
-        to modify <varname>kern.ipc.nsfbufs</varname> sysctl.  This sysctl
-        variable controls the number of filesystem buffers &man.sendfile.2;
-        is allowed to use for performing it's work.  This parameter nominally
-        scales with <varname>kern.maxusers</varname> so you should not need
-        to modify it.</para>
+      <para>For busy servers that make extensive use of the
+	&man.sendfile.2; system call, it may be necessary to increase
+	the number of &man.sendfile.2; buffers via the
+	<option>NSFBUFS</option> kernel configuration option.  A
+	common indicator that this parameter needs to be adjusted is
+	when processes are seen in the <errorname>sfbufa</errorname>
+	state.  The sysctl variable
+	<varname>kern.ipc.nsfbufs</varname> is a read-only glimpse at
+	the kernel configured variable.  This parameter nominally
+	scales with <varname>kern.maxusers</varname>, however it may
+	be necessary to tune accordingly.</para>
+
+      <important>
+	<para>Even though a socket has been marked as non-blocking,
+	  calling &man.sendfile.2; on the non-blocking socket may
+	  result in the &man.sendfile.2; call blocking until enough
+	  <literal>struct sf_buf</literal>'s are made
+	  available.</para>
+      </important>
 
       <sect3>
 	<title><varname>net.inet.ip.portrange.*</varname></title>