Document how to turn off disk write cache on popular operating systems.

diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index a1a327743433c1a79badbe127357d2ff5a8ae842..55cd6b1d6b82619189c8edd56977b4b490411b7a 100644 (file)
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -1,4 +1,4 @@
-
+
 
 
  Reliability and the Write-Ahead Log
@@ -58,8 +58,17 @@
    while some are write-back, and the
    same concerns about data loss exist for write-back drive caches as
    exist for disk controller caches.  Consumer-grade IDE drives are
-   particularly likely to contain write-back caches that will not
-   survive a power failure.
+   particularly likely to have write-back caches that will not survive a
+   power failure.  To check write caching on Linux use
+   hdparm -I;  it is enabled if there is a * next
+   to Write cache.  hdparm -W can to turn off
+   write caching.  On FreeBSD use
+   atacontrol.  (For SCSI disks use 
+   url="http://sg.torque.net/sg/sdparm.html">sdparm
+   to turn off WCE.)  On Windows write caching is
+   controlled by My Computer\Open\{select disk
+   drive}\Properties\Hardware\Properties\Policies\Enable write caching on
+   the disk.