svn commit: r40228 - head/en_US.ISO8859-1/books/faq

[Eitan Adler]

Author: eadler
Date: Sat Dec  1 17:00:17 2012
New Revision: 40228
URL: http://svnweb.freebsd.org/changeset/doc/40228

Log:
  Update and clarify the FAQ on soft-updates.
  
  Noted by:	-stable mailing list
  Approved by:	bcr (mentor)

Modified:
  head/en_US.ISO8859-1/books/faq/book.xml

Modified: head/en_US.ISO8859-1/books/faq/book.xml
==============================================================================
--- head/en_US.ISO8859-1/books/faq/book.xml	Sat Dec  1 15:51:31 2012	(r40227)
+++ head/en_US.ISO8859-1/books/faq/book.xml	Sat Dec  1 17:00:17 2012	(r40228)
@@ -4489,24 +4489,25 @@ kern.sched.name: ULE</screen>
 	<question id="safe-softupdates">
 	  <para>Which partitions can safely use Soft Updates?  I have
 	    heard that Soft Updates on <filename class="directory">/</filename> can cause
-	    problems.</para>
+	    problems.  What about Journaled Soft Updates?</para>
 	</question>
 
 	<answer>
 	  <para>Short answer: you can usually use Soft Updates safely on
 	    all partitions.</para>
 
-	  <para>Long answer: There used to be some concern over using
-	    Soft Updates on the root partition.  Soft Updates has two
-	    characteristics that caused this.  First, a Soft Updates
+	  <para>Long answer:  Soft Updates has two
+	    characteristics that may be undesirable on certain
+	    paritions.  First, a Soft Updates
 	    partition has a small chance of losing data during a system
 	    crash.  (The partition will not be corrupted; the data will
-	    simply be lost.) Also, Soft Updates can cause temporary
+	    simply be lost.)  Second, Soft Updates can cause temporary
 	    space shortages.</para>
 
 	  <para>When using Soft Updates, the kernel can take up to
-	    thirty seconds to actually write changes to the physical
-	    disk.  If you delete a large file, the file still resides on
+	    thirty seconds to write changes to the physical
+	    disk.  When a large file is deleted the file still
+	    resides on
 	    disk until the kernel actually performs the deletion.  This
 	    can cause a very simple race condition.  Suppose you delete
 	    one large file and immediately create another large file.
@@ -4522,20 +4523,14 @@ kern.sched.name: ULE</screen>
 
 	  <para>If a system should crash after the kernel accepts a
 	    chunk of data for writing to disk, but before that data is
-	    actually written out, data could be lost or corrupted.  This
-	    risk is extremely small, but generally manageable.  Use of
-	    IDE write caching greatly increases this risk; it is
-	    strongly recommended that you disable IDE write caching when
-	    using Soft Updates.</para>
+	    actually written out, data could be lost.  This
+	    risk is extremely small, but generally manageable.</para>
 
 	  <para>These issues affect all partitions using Soft Updates.
 	    So, what does this mean for the root partition?</para>
 
 	  <para>Vital information on the root partition changes very
-	    rarely.  Files such as
-	    <filename>/boot/kernel/kernel</filename> and the contents of
-	    <filename class="directory">/etc</filename> only change during system
-	    maintenance, or when users change their passwords.  If the
+	    rarely.  If the
 	    system crashed during the thirty-second window after such a
 	    change is made, it is possible that data could be lost.
 	    This risk is negligible for most applications, but you
@@ -4551,6 +4546,10 @@ kern.sched.name: ULE</screen>
 	    problems.  Symlinking <filename class="directory">/tmp</filename> to
 	    <filename class="directory">/var/tmp</filename> will solve this
 	    problem.</para>
+
+	  <para>Finally, &man.dump.8; does not work in live mode (-L)
+	    on a filesystem, with Journaled Soft Updates
+	    (<acronym>SU+J</acronym>).</para>
 	</answer>
       </qandaentry>