-<!-- $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>
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