gsg_txn/C/hotfailover.html

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            <h2 class="title" style="clear: both"><a id="hotfailover"></a>Using Hot Failovers</h2>
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      <p>
            You can maintain a backup that can be used for failover purposes.
            Hot failovers differ from the backup and restore
            procedures described previously in this chapter in that data
            used for traditional backups is typically copied to offline storage.
            Recovery time for a traditional backup is determined by:
        </p>
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                    How quickly you can retrieve that storage media.
                    Typically storage media for critical backups is moved
                    to a safe facility in a remote location, so this step can
                    take a relatively long time.
                </p>
          </li>
          <li>
            <p>
                    How fast you can read the backup from the storage media
                    to a local disk drive. If you have very large backups,
                    or if your storage media is very slow, this can be a
                    lengthy process.
                </p>
          </li>
          <li>
            <p>
                    How long it takes you to run catastrophic recovery
                    against the newly restored backup. As described earlier
                    in this chapter, this process can be lengthy because
                    every log file must be examined during the recovery
                    process.
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      <p>
            When you use a hot failover, the backup is maintained
            at a location that is reasonably fast to access. Usually, this
            is a second disk drive local to the machine.
            In this situation, recovery time is very quick
            because you only have to reopen your
            environment and database, using the failover environment
            for the environment open.
        </p>
      <p>
            Hot failovers obviously do not protect you from truly
            catastrophic disasters (such as a fire in your machine room)
            because the backup is still local to the machine. However,
            you can guard against more mundane problems (such as a broken
            disk drive) by keeping the backup on a
            second drive that is managed by an alternate disk controller.
        </p>
      <p>
            To maintain a hot failover:
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                    Copy all the active database files to the failover
                    directory.  Use the <span><b class="command">db_archive</b></span>
                    command line utility with the
                    <tt class="literal">-s</tt> option to identify all the active
                    database files.
                </p>
          </li>
          <li>
            <p>
                    Identify all the inactive log files in your production
                    environment and <span class="emphasis"><em>move</em></span> these to the failover
                    directory.  Use the <span><b class="command">db_archive</b></span>
                    command with no command line options to obtain a list
                    of these log files.
                </p>
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          <li>
            <p>
                    Identify the active log files in your production
                    environment, and <span class="emphasis"><em>copy</em></span> these to the
                    failover directory. Use the
                    <span><b class="command">db_archive</b></span> command with the
                    <tt class="literal">-l</tt> option to obtain a list of these
                    log files.
                </p>
          </li>
          <li>
            <p>
                    Run catastrophic recovery against the failover
                    directory. Use the <span><b class="command">db_recover</b></span>
                    command with the <tt class="literal">-c</tt> option to do
                    this.
                </p>
          </li>
          <li>
            <p>
                    Optionally copy the backup to an archival location.
                </p>
          </li>
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      <p>
            Once you have performed this procedure, you can maintain an
            active hot backup by repeating steps 2 - 5 as often
            as is required by your application.
        </p>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
                If you perform step 1, steps 2-5 must follow in order to
                ensure consistency of your hot backup.
            </p>
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      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
            Rather than use the previous procedure, you can use the <span><b class="command">db_hotbackup</b></span> command line utility
            to do the same thing. This utility will (optionally) run a checkpoint and then copy all necessary files to a target
            directory for you.
        </p>
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      <p>
            To actually perform a failover, simply:
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                    Shut down all processes which are running against the original environment.
                </p>
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            <p>
                    If you have an archival copy of the backup environment, you can optionally try copying the remaining
                    log files from the original environment and running catastrophic recovery against that backup
                    environment. Do this <span class="emphasis"><em>only</em></span> if you have a an archival copy of the backup
                    environment.
                </p>
            <p>
                    This step can allow you to recover data created or modified in the original environment, but which
                    did not have a chance to be reflected in the hot backup environment.
                </p>
          </li>
          <li>
            <p>
                    Reopen your environment and databases as normal, but use
                    the backup environment instead of the production
                    environment.
                </p>
          </li>
        </ol>
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