systemd-readahead-replay.service.xml 5.03 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

24
<refentry id="systemd-readahead-replay.service" conditional='ENABLE_READAHEAD'>
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

        <refentryinfo>
                <title>systemd-readahead-replay.service</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>systemd-readahead-replay.service</refentrytitle>
                <manvolnum>8</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd-readahead-replay.service</refname>
                <refname>systemd-readahead-collect.service</refname>
                <refname>systemd-readahead-done.service</refname>
                <refname>systemd-readahead-done.timer</refname>
                <refname>systemd-readahead</refname>
51
                <refpurpose>Disk read ahead logic</refpurpose>
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>systemd-readahead-replay.service</filename></para>
                <para><filename>systemd-readahead-collect.service</filename></para>
                <para><filename>systemd-readahead-done.service</filename></para>
                <para><filename>systemd-readahead-done.timer</filename></para>
                <para><filename>/usr/lib/systemd/systemd-readahead</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><filename>systemd-readahead-collect.service</filename>
                is a service that collects disk usage patterns at boot
                time. <filename>systemd-readahead-replay.service</filename>
                is a service that replays this access data collected
                at the subsequent boot. Since disks tend to be
                magnitudes slower than RAM this is intended to improve
                boot speeds by pre-loading early at boot all data on
                disk that is known to be read for the complete boot
                process.</para>

                <para><filename>systemd-readahead-done.service</filename>
                is executed a short while after boot completed and signals
                <filename>systemd-readahead-collect.service</filename>
                to end data collection. On this signal this service
                will then sort the collected disk accesses and store
                information about them disk in
                <filename>/.readahead</filename>.</para>

                <para>Normally, both
                <filename>systemd-readahead-collect.service</filename>
                and
                <filename>systemd-readahead-replay.service</filename>
                are activated at boot so that access patterns from the
Ville Skyttä's avatar
Ville Skyttä committed
88
                preceding boot are replayed and new data collected
89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113
                for the subsequent boot. However, on read-only media
                where the collected data cannot be stored it might
                be a good idea to disable
                <filename>systemd-readahead-collect.service</filename>.</para>

                <para>On rotating media, when replaying disk accesses
                at early boot
                <filename>systemd-readahead-replay.service</filename>
                will order read requests by their location on disk. On
                non-rotating media, they will be ordered by their
                original access timestamp. If the file system supports
                it
                <filename>systemd-readahead-collect.service</filename>
                will also defragment and rearrange files on disk to
                optimize subsequent boot times.</para>
        </refsect1>

        <refsect1>
                <title>See Also</title>
                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>