From adfb44458163bf749a2ec04db52ae88051cca498 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Sat, 27 Feb 2010 01:39:46 +0000
Subject: [PATCH] Document ATAPI drive flush command, and mention SSD drives.
---
doc/src/sgml/wal.sgml | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 5f6a6eb2e18..9e9489da156 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.62 2010/02/20 18:28:37 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.63 2010/02/27 01:39:46 momjian Exp $ -->
<chapter id="wal">
<title>Reliability and the Write-Ahead Log</title>
@@ -59,8 +59,11 @@
same concerns about data loss exist for write-back drive caches as
exist for disk controller caches. Consumer-grade IDE and SATA drives are
particularly likely to have write-back caches that will not survive a
- power failure. Many solid-state drives also have volatile write-back
- caches. To check write caching on <productname>Linux</> use
+ power failure, though <acronym>ATAPI-6</> introduced a drive cache
+ flush command that some file systems use, e.g. <acronym>ZFS</>.
+ Many solid-state drives also have volatile write-back
+ caches, and many do not honor cache flush commands by default.
+ To check write caching on <productname>Linux</> use
<command>hdparm -I</>; it is enabled if there is a <literal>*</> next
to <literal>Write cache</>; <command>hdparm -W</> to turn off
write caching. On <productname>FreeBSD</> use
--
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