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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 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 51 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 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>The Backup Process</title><link rel="stylesheet" type="text/css" href="styles.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Cedar Backup 2 Software Manual"><link rel="up" href="ch02.html" title="Chapter 2. Basic Concepts"><link rel="prev" href="ch02s03.html" title="Cedar Backup Pools"><link rel="next" href="ch02s05.html" title="Coordination between Master and Clients"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">The Backup Process</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s03.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Basic Concepts</th><td width="20%" align="right"> <a accesskey="n" href="ch02s05.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="cedar-basic-process"></a>The Backup Process</h2></div></div></div><p>
The Cedar Backup backup process is structured in terms of a set of
decoupled actions which execute independently (based on a schedule in
<span class="command"><strong>cron</strong></span>) rather than through some highly coordinated
flow of control.
</p><p>
This design decision has both positive and negative consequences. On
the one hand, the code is much simpler and can choose to simply abort
or log an error if its expectations are not met. On the other hand,
the administrator must coordinate the various actions during initial
set-up. See <a class="xref" href="ch02s05.html" title="Coordination between Master and Clients">the section called “Coordination between Master and Clients”</a> (later in this
chapter) for more information on this subject.
</p><p>
A standard backup run consists of four steps (actions), some of which
execute on the master machine, and some of which execute on one or
more client machines. These actions are:
<em class="firstterm">collect</em>, <em class="firstterm">stage</em>,
<em class="firstterm">store</em> and <em class="firstterm">purge</em>.
</p><p>
In general, more than one action may be specified on the command-line.
If more than one action is specified, then actions will be taken in a
sensible order (generally collect, stage, store, purge). A special
<em class="firstterm">all</em> action is also allowed, which implies all
of the standard actions in the same sensible order.
</p><p>
The <span class="command"><strong>cback</strong></span> command also supports several actions
that are not part of the standard backup run and cannot be executed
along with any other actions. These actions are
<em class="firstterm">validate</em>, <em class="firstterm">initialize</em> and
<em class="firstterm">rebuild</em>. All of the various actions are
discussed further below.
</p><p>
See <a class="xref" href="ch05.html" title="Chapter 5. Configuration">Chapter 5, <i>Configuration</i></a> for more information on how a
backup run is configured.
</p><div class="sidebar"><div class="titlepage"><div><div><p class="title"><b>Flexibility</b></p></div></div></div><p>
Cedar Backup was designed to be flexible. It allows you to decide
for yourself which backup steps you care about executing (and when
you execute them), based on your own situation and your own
priorities.
</p><p>
As an example, I always back up every machine I own. I typically
keep 7-10 days of staging directories around, but switch CD/DVD media
mostly every week. That way, I can periodically take a disc
off-site in case the machine gets stolen or damaged.
</p><p>
If you're not worried about these risks, then there's no need to
write to disc. In fact, some users prefer to use their master
machine as a simple <span class="quote">“<span class="quote">consolidation point</span>”</span>. They don't
back up any data on the master, and don't write to disc at all.
They just use Cedar Backup to handle the mechanics of moving
backed-up data to a central location. This isn't quite what Cedar
Backup was written to do, but it is flexible enough to meet their
needs.
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-collect"></a>The Collect Action</h3></div></div></div><p>
The collect action is the first action in a standard backup run.
It executes on both master and client nodes. Based on configuration,
this action traverses the peer's filesystem and gathers files to be
backed up. Each configured high-level directory is collected up
into its own <span class="command"><strong>tar</strong></span> file in the <em class="firstterm">collect
directory</em>. The tarfiles can either be uncompressed
(<code class="filename">.tar</code>) or compressed with either
<span class="command"><strong>gzip</strong></span> (<code class="filename">.tar.gz</code>) or
<span class="command"><strong>bzip2</strong></span> (<code class="filename">.tar.bz2</code>).
</p><p>
There are three supported collect modes:
<em class="firstterm">daily</em>, <em class="firstterm">weekly</em> and
<em class="firstterm">incremental</em>. Directories configured for
daily backups are backed up every day. Directories configured for
weekly backups are backed up on the first day of the week.
Directories configured for incremental backups are traversed every
day, but only the files which have changed (based on a saved-off
<em class="firstterm">SHA hash</em>) are actually backed up.
</p><p>
Collect configuration also allows for a variety of ways to filter
files and directories out of the backup. For instance,
administrators can configure an <em class="firstterm">ignore indicator
file</em>
<a href="#ftn.idp59530672" class="footnote" name="idp59530672"><sup class="footnote">[9]</sup></a>
or specify absolute paths or filename patterns
<a href="#ftn.idp59531904" class="footnote" name="idp59531904"><sup class="footnote">[10]</sup></a>
to be excluded. You can even configure a backup <span class="quote">“<span class="quote">link
farm</span>”</span> rather than explicitly listing files and directories
in configuration.
</p><p>
This action is optional on the master. You only need to configure
and execute the collect action on the master if you have data to
back up on that machine. If you plan to use the master only as a
<span class="quote">“<span class="quote">consolidation point</span>”</span> to collect data from other
machines, then there is no need to execute the collect action
there. If you run the collect action on the master, it behaves the
same there as anywhere else, and you have to stage the master's
collected data just like any other client (typically by configuring
a local peer in the stage action).
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-stage"></a>The Stage Action</h3></div></div></div><p>
The stage action is the second action in a standard backup run. It
executes on the master peer node. The master works down the list of
peers in its backup pool and stages (copies) the collected backup
files from each of them into a daily staging directory by peer
name.
</p><p>
For the purposes of this action, the master node can be configured
to treat itself as a client node. If you intend to back up data on
the master, configure the master as a local peer. Otherwise, just
configure each of the clients as a remote peer.
</p><p>
Local and remote client peers are treated differently. Local peer
collect directories are assumed to be accessible via normal copy
commands (i.e. on a mounted filesystem) while remote peer collect
directories are accessed via an <em class="firstterm">RSH-compatible</em>
command such as <span class="command"><strong>ssh</strong></span>.
</p><p>
If a given peer is not ready to be staged, the stage process will
log an error, abort the backup for that peer, and then move on to
its other peers. This way, one broken peer cannot break a backup
for other peers which are up and running.
</p><p>
Keep in mind that Cedar Backup is flexible about what actions must
be executed as part of a backup. If you would prefer, you can stop
the backup process at this step, and skip the store step. In this
case, the staged directories will represent your backup rather than
a disc.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Directories <span class="quote">“<span class="quote">collected</span>”</span> by another process can be
staged by Cedar Backup. If the file
<code class="filename">cback.collect</code> exists in a collect directory
when the stage action is taken, then that directory will be
staged.
</p></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-store"></a>The Store Action</h3></div></div></div><p>
The store action is the third action in a standard backup run. It
executes on the master peer node. The master machine determines the
location of the current staging directory, and then writes the
contents of that staging directory to disc. After the contents of
the directory have been written to disc, an optional validation
step ensures that the write was successful.
</p><p>
If the backup is running on the first day of the week, if the drive
does not support multisession discs, or if the
<code class="option">--full</code> option is passed to the
<span class="command"><strong>cback</strong></span> command, the disc will be rebuilt from
scratch. Otherwise, a new ISO session will be added to the disc
each day the backup runs.
</p><p>
This action is entirely optional. If you would prefer to just
stage backup data from a set of peers to a master machine, and have
the staged directories represent your backup rather than a disc,
this is fine.
</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>
The store action is not supported on the Mac OS X (darwin)
platform. On that platform, the <span class="quote">“<span class="quote">automount</span>”</span>
function of the Finder interferes significantly with Cedar
Backup's ability to mount and unmount media and write to the CD
or DVD hardware. The Cedar Backup writer and image
functionality works on this platform, but the effort required to
fight the operating system about who owns the media and the
device makes it nearly impossible to execute the store action
successfully.
</p></div><div class="sidebar"><div class="titlepage"><div><div><p class="title"><b>Current Staging Directory</b></p></div></div></div><p>
The store action tries to be smart about finding the current
staging directory. It first checks the current day's staging
directory. If that directory exists, and it has not yet been
written to disc (i.e. there is no store indicator), then it will
be used. Otherwise, the store action will look for an unused
staging directory for either the previous day or the next day,
in that order. A warning will be written to the log under
these circumstances (controlled by the <warn_midnite>
configuration value).
</p><p>
This behavior varies slightly when the <code class="option">--full</code>
option is in effect. Under these circumstances, any existing
store indicator will be ignored. Also, the store action will
always attempt to use the current day's staging directory,
ignoring any staging directories for the previous day or the
next day. This way, running a full store action more than once
concurrently will always produce the same results. (You might
imagine a use case where a person wants to make several copies
of the same full backup.)
</p></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-purge"></a>The Purge Action</h3></div></div></div><p>
The purge action is the fourth and final action in a standard
backup run. It executes both on the master and client peer nodes.
Configuration specifies how long to retain files in certain
directories, and older files and empty directories are purged.
</p><p>
Typically, collect directories are purged daily, and stage
directories are purged weekly or slightly less often (if a disc
gets corrupted, older backups may still be available on the
master). Some users also choose to purge the configured working
directory (which is used for temporary files) to eliminate any
leftover files which might have resulted from changes to
configuration.
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-all"></a>The All Action</h3></div></div></div><p>
The all action is a pseudo-action which causes all of the actions
in a standard backup run to be executed together in order. It
cannot be combined with any other actions on the command line.
</p><p>
Extensions <span class="emphasis"><em>cannot</em></span> be executed as part of the
all action. If you need to execute an extended action, you must
specify the other actions you want to run individually on the
command line. <a href="#ftn.idp59558576" class="footnote" name="idp59558576"><sup class="footnote">[11]</sup></a>
</p><p>
The all action does not have its own configuration. Instead, it
relies on the individual configuration sections for all of the
other actions.
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-validate"></a>The Validate Action</h3></div></div></div><p>
The validate action is used to validate configuration
on a particular peer node, either master or client. It cannot be
combined with any other actions on the command line.
</p><p>
The validate action checks that the configuration file can be
found, that the configuration file is valid, and that certain
portions of the configuration file make sense (for instance, making
sure that specified users exist, directories are readable and
writable as necessary, etc.).
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-initialize"></a>The Initialize Action</h3></div></div></div><p>
The initialize action is used to initialize media for use with
Cedar Backup. This is an optional step. By default, Cedar Backup
does not need to use initialized media and will write to whatever
media exists in the writer device.
</p><p>
However, if the <span class="quote">“<span class="quote">check media</span>”</span> store configuration
option is set to true, Cedar Backup will check the media before
writing to it and will error out if the media has not been
initialized.
</p><p>
Initializing the media consists of writing a mostly-empty image
using a known media label (the media label will begin with
<span class="quote">“<span class="quote">CEDAR BACKUP</span>”</span>).
</p><p>
Note that only rewritable media (CD-RW, DVD+RW) can be initialized.
It doesn't make any sense to initialize media that cannot be
rewritten (CD-R, DVD+R), since Cedar Backup would then not be able
to use that media for a backup. You can still configure Cedar
Backup to check non-rewritable media; in this case, the check will
also pass if the media is apparently unused (i.e. has no media
label).
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="cedar-basic-process-rebuild"></a>The Rebuild Action</h3></div></div></div><p>
The rebuild action is an exception-handling action that is executed
independent of a standard backup run. It cannot be combined with
any other actions on the command line.
</p><p>
The rebuild action attempts to rebuild <span class="quote">“<span class="quote">this week's</span>”</span>
disc from any remaining unpurged staging directories. Typically,
it is used to make a copy of a backup, replace lost or damaged
media, or to switch to new media mid-week for some other reason.
</p><p>
To decide what data to write to disc again, the rebuild action
looks back and finds the first day of the current week. Then, it finds
any remaining staging directories between that date and the current
date. If any staging directories are found, they are all written
to disc in one big ISO session.
</p><p>
The rebuild action does not have its own configuration. It relies
on configuration for other other actions, especially the store
action.
</p></div><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idp59530672" class="footnote"><p><a href="#idp59530672" class="para"><sup class="para">[9] </sup></a>Analagous to <code class="filename">.cvsignore</code> in CVS</p></div><div id="ftn.idp59531904" class="footnote"><p><a href="#idp59531904" class="para"><sup class="para">[10] </sup></a>In terms of Python regular expressions</p></div><div id="ftn.idp59558576" class="footnote"><p><a href="#idp59558576" class="para"><sup class="para">[11] </sup></a>Some users find this surprising,
because extensions are configured with sequence numbers. I did it
this way because I felt that running extensions as part of the all
action would sometimes result in surprising behavior. I am not
planning to change the way this works.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s05.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Cedar Backup Pools </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Coordination between Master and Clients</td></tr></table></div></body></html>
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