diff --git a/doc/src/sgml/manage-ag.sgml b/doc/src/sgml/manage-ag.sgml
new file mode 100644
index b44d521..78ec509
*** a/doc/src/sgml/manage-ag.sgml
--- b/doc/src/sgml/manage-ag.sgml
*************** dropdb <replaceable class="parameter">db
*** 379,395 ****
     expensive, slower disk system.
    </para>
  
    <para>
     To define a tablespace, use the <xref
     linkend="sql-createtablespace">
     command, for example:<indexterm><primary>CREATE TABLESPACE</></>:
  <programlisting>
! CREATE TABLESPACE fastspace LOCATION '/mnt/sda1/postgresql/data';
  </programlisting>
     The location must be an existing, empty directory that is owned by
     the <productname>PostgreSQL</> operating system user.  All objects subsequently
     created within the tablespace will be stored in files underneath this
!    directory.
    </para>
  
    <note>
--- 379,412 ----
     expensive, slower disk system.
    </para>
  
+   <warning>
+    <para>
+      Even though located outside the main PostgreSQL data directory,
+      tablespaces are an integral part of the database cluster and
+      <emphasis>cannot</emphasis> be treated as an autonomous collection
+      of data files. They are dependent on metadata contained in the main
+      data directory, and therefore cannot be attached to a different
+      database cluster or backed up individually.  Similarly, if you lose
+      a tablespace (file deletion, disk failure, etc), the database cluster
+      might become unreadable or unable to start.  Placing a tablespace
+      on a temporary file system like a ramdisk risks the reliability of
+      the entire cluster.
+    </para>
+   </warning>
+ 
    <para>
     To define a tablespace, use the <xref
     linkend="sql-createtablespace">
     command, for example:<indexterm><primary>CREATE TABLESPACE</></>:
  <programlisting>
! CREATE TABLESPACE fastspace LOCATION '/ssd1/postgresql/data';
  </programlisting>
     The location must be an existing, empty directory that is owned by
     the <productname>PostgreSQL</> operating system user.  All objects subsequently
     created within the tablespace will be stored in files underneath this
!    directory.  The location must not be on removable or transient storage,
!    as the cluster might fail to function if the tablespace is missing
!    or lost.
    </para>
  
    <note>
diff --git a/doc/src/sgml/ref/create_tablespace.sgml b/doc/src/sgml/ref/create_tablespace.sgml
new file mode 100644
index b643565..cf6215e
*** a/doc/src/sgml/ref/create_tablespace.sgml
--- b/doc/src/sgml/ref/create_tablespace.sgml
*************** CREATE TABLESPACE <replaceable class="pa
*** 50,55 ****
--- 50,63 ----
     <command>CREATE INDEX</> or <command>ADD CONSTRAINT</> to have the data
     files for these objects stored within the specified tablespace.
    </para>
+ 
+   <warning>
+    <para>
+     A tablespace cannot be used independently of the cluster in which it
+     is defined;  see <xref linkend="manage-ag-tablespaces"/>.
+    </para>
+   </warning>
+ 
   </refsect1>
  
   <refsect1>