</para>

<para>

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

<application>atacontrol</>. (For SCSI disks use <ulink

url="http://sg.danny.cz/sg/sdparm.html"><application>sdparm</></ulink>

to turn off <literal>WCE</>.) On <productname>Solaris</> the disk

write cache is controlled by <ulink

url="http://www.sun.com/bigadmin/content/submitted/format_utility.jsp"><literal>format

-e</></ulink>. (The Solaris <acronym>ZFS</> file system is safe with

disk write-cache enabled because it issues its own disk cache flush

commands.) On <productname>Windows</> if <varname>wal_sync_method</>

is <literal>open_datasync</> (the default), write caching is disabled

by unchecking <literal>My Computer\Open\{select disk

drive}\Properties\Hardware\Properties\Policies\Enable write caching on

the disk</>. Also on Windows, <literal>fsync</> and

<literal>fsync_writethrough</> never do write caching. The

<literal>fsync_writethrough</> option can also be used to disable

write caching on <productname>MacOS X</>.

</para>

These caches can typically be disabled; however, the method for doing

this varies by operating system and drive type:

</para>

<itemizedlist>

<listitem>

<para>

On <productname>Linux</>, IDE drives can be queried using

<command>hdparm -I</command>; write caching is enabled if there is

a <literal>*</> next to <literal>Write cache</>. <command>hdparm -W</>

can be used to turn off write caching. SCSI drives can be queried

using <ulink url="http://sg.danny.cz/sg/sdparm.html"><application>sdparm</></ulink>.

for SCSI drives. Use <command>sdparm --get=WCE</command> to check

whether the write cache is enabled and <command>sdparm --clear=WCE</>

to disable it.

</para>

</listitem>

<listitem>

<para>

On <productname>FreeBSD</>, IDE drives can be queried using

<command>atacontrol</command>, and SCSI drives using

<command>sdparm</command>.

</para>

</listitem>

<listitem>

<para>

On <productname>Solaris</>, the disk write cache is controlled by

<ulink url="http://www.sun.com/bigadmin/content/submitted/format_utility.jsp"><literal>format -e</></ulink>.

(The Solaris <acronym>ZFS</> file system is safe with disk write-cache

enabled because it issues its own disk cache flush commands.)

</para>

</listitem>

<listitem>

<para>

On <productname>Windows</>, if <varname>wal_sync_method</> is

<literal>open_datasync</> (the default), write caching is disabled

by unchecking <literal>My Computer\Open\{select disk drive}\Properties\Hardware\Properties\Policies\Enable write caching on the disk</>.

Alternatively, set <varname>wal_sync_method</varname> to <literal>fsync</> or <literal>fsync_writethrough</>, which never do write caching.

</para>

</listitem>

<listitem>

<para>

On <productname>MacOS X</productname>, write caching can be disabled by

setting <varname>wal_sync_method</> to <literal>fsync_writethrough</>.

</para>

</listitem>

</itemizedlist>

<para>

Many file systems that use write barriers (e.g. <acronym>ZFS</>,