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<chapter id="wal">

<title>Reliability and the Write-Ahead Log</title>

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 <productname>Linux</> use

<command>hdparm -I</>; it is enabled if there is a <literal>*</> next

to <literal>Write cache</>. <command>hdparm -W</> can to turn off

write caching. On <productname>FreeBSD</> use

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

url="http://sg.torque.net/sg/sdparm.html"><application>sdparm</></ulink>

to turn off <literal>WCE</>.) On <productname>Windows</> write caching is

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

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

the disk</>.

</para>

<para>