Index: svn_1.5_releasenotes.html
===================================================================
--- svn_1.5_releasenotes.html	(revision 29775)
+++ svn_1.5_releasenotes.html	(working copy)
@@ -38,6 +38,7 @@
   <li>Changelist support</li>
   <li>Relative and peg URLs in <tt>svn:externals</tt></li>
   <li>FSFS sharding</li>
+  <li>FSFS immutable file separation</li>
   <li>Command-line client improvements</li>
   <li>API changes, improvements and language bindings</li>
   <li>Easier to try out experimental <tt>ra_serf</tt> DAV access module</li>
@@ -707,10 +708,11 @@
 but of course, Subversion 1.5 will be able to continue using repositories
 employing the older scheme without any problem.</p>
 
-<p>The primary reason for the change is to help support filesystems with
-less-than-ideal large directory entry count performance.  In addition,
-certain third-party tools may work better with a sharded layout versus
-an unsharded one.</p>
+<p>The primary reason for the change is to allow the revision count to
+grow beyond the filesystem's (efficient) directory entry limit.  While
+modern filesystems can support millions of entries per directory, they
+become slower and common administrative tools (e.g. directory
+listings, backups) become unwieldy or fail completely.</p>
 
 <p>For more information about the technical underpinnings of FSFS sharding, 
 see this <a href="http://www.farside.org.uk/200704/tree_structured_fsfs">blog
@@ -723,8 +725,36 @@
 -->
 </p>
 
+<p>The shard size can by adjusted by editing the "layout sharded" line
+in "db/format" after <code>svnadmin create</code> but before
+populating the repository.</p>
+
 </div>  <!-- fsfs-sharding -->
 
+<div class="h3" id="fsfs-isolate-immutable" title="fsfs-isolate-immutable">
+<h3>FSFS Immutable File Separation (<em>server</em>)</h3>
+
+<p>The FSFS repositories never change a revision after it is written
+to the disk.  This should allow the operating system to cache these
+files forever, but certain filesystems (e.g. NFS) prohibit such
+caching by default.  The FSFS repository layout has been changed such
+that the immutable files are confined to the directories "db/revs" and
+"db/txn-protorevs".  This allows these directories to be on a mount
+point where caching is enabled (on Linux look at the "nocto" option to
+nfs(5)).</p>
+
+<p>Since commit transactions are now built up in "db/txn-protorevs"
+instead of "db/transactions", the latter directory no longer needs to
+be on the same mount point.  If the repository is stored on a slower
+filesystem (e.g. NFS), then commit performance can be improved by
+moving the transactions directory to local disk (using a symbolic
+link).  If you are using multiple svn servers behind a network load
+scaler, you must configure the load scaler to direct to the same
+server for the duration of the transaction.  This is typically called
+"client affinity".</p>
+
+</div>  <!-- fsfs-isolate-immutable -->
+
 </div>  <!-- new-features -->