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Document ATAPI drive flush command, and mention SSD drives.

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Bruce Momjian 2010-02-27 01:39:46 +00:00
parent 4b0f822c77
commit adfb444581
1 changed files with 6 additions and 3 deletions
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doc/src/sgml/wal.sgml
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<!-- $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