<productname>PostgreSQL</> periodically writes full page images to

permanent WAL storage <emphasis>before</> modifying the actual page on

disk. By doing this, during crash recovery <productname>PostgreSQL</> can

restore partially-written pages from WAL. If you have a battery-backed disk

controller or file-system software that prevents partial page writes

(e.g., ZFS), you can safely turn off this page imaging by turning off the

<xref linkend="guc-full-page-writes"> parameter.

restore partially-written pages from WAL. If you have file-system software

that prevents partial page writes (e.g., ZFS), you can turn off

this page imaging by turning off the <xref

linkend="guc-full-page-writes"> parameter. Battery-Backed Unit

(BBU) disk controllers do not prevent partial page writes unless

they guarantee that data is written to the BBU as full (8kB) pages.

</para>

</sect1>