openstack-manuals/doc/common/section_objectstorage-troubleshoot.xml

<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
  xmlns:xi="http://www.w3.org/2001/XInclude"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  version="5.0"
  xml:id="troubleshooting-openstack-object-storage">
    <title>Troubleshoot Object Storage</title>
    <para>For Object Storage, everything is logged in <filename>/var/log/syslog</filename> (or messages on some distros).
        Several settings enable further customization of logging, such as <literal>log_name</literal>, <literal>log_facility</literal>,
        and <literal>log_level</literal>, within the object server configuration files.</para>
    <section xml:id="drive-failure">
        <title>Drive failure</title>
        <para>In the event that a drive has failed, the first step is to make sure the drive is
            unmounted. This will make it easier for Object Storage to work around the failure until
            it has been resolved. If the drive is going to be replaced immediately, then it is just
            best to replace the drive, format it, remount it, and let replication fill it up.</para>
        <para>If the drive can’t be replaced immediately, then it is best to leave it
            unmounted, and remove the drive from the ring. This will allow all the replicas
            that were on that drive to be replicated elsewhere until the drive is replaced.
            Once the drive is replaced, it can be re-added to the ring.</para>
        <para>You can look at error messages in <filename>/var/log/kern.log</filename> for hints of drive failure.</para>
    </section>
    <section xml:id="server-failure">
        <title>Server failure</title>
        <para>If a server is having hardware issues, it is a good idea to make sure the
            Object Storage services are not running. This will allow Object Storage to
            work around the failure while you troubleshoot.</para>
        <para>If the server just needs a reboot, or a small amount of work that should only
            last a couple of hours, then it is probably best to let Object Storage work
            around the failure and get the machine fixed and back online. When the machine
            comes back online, replication will make sure that anything that is missing
            during the downtime will get updated.</para>
        <para>If the server has more serious issues, then it is probably best to remove all
            of the server’s devices from the ring. Once the server has been repaired and is
            back online, the server’s devices can be added back into the ring. It is
            important that the devices are reformatted before putting them back into the
            ring as it is likely to be responsible for a different set of partitions than
            before.</para>
    </section>
    <section xml:id="detect-failed-drives">
        <title>Detect failed drives</title>
        <para>It has been our experience that when a drive is about to fail, error messages will spew into
            /var/log/kern.log. There is a script called swift-drive-audit that can be run via cron
            to watch for bad drives. If errors are detected, it will unmount the bad drive, so that
            Object Storage can work around it. The script takes a configuration file with the
            following settings:</para>
        <xi:include href="tables/swift-drive-audit-drive-audit.xml"/>
        <para>This script has only been tested on Ubuntu 10.04, so if you are using a
            different distro or OS, some care should be taken before using in production.
        </para>
    </section>
    <section xml:id="recover-ring-builder-file">
        <title>Emergency recovery of ring builder files</title>
        <para>You should always keep a backup of swift ring builder files. However, if an
            emergency occurs, this procedure may assist in returning your cluster to an
            operational state.</para>
        <para>Using existing swift tools, there is no way to recover a builder file from a
            <filename>ring.gz</filename> file. However, if you have a knowledge of Python, it is possible to
            construct a builder file that is pretty close to the one you have lost. The
            following is what you will need to do.</para>
        <warning>
            <para>This procedure is a last-resort for emergency circumstances. It
                requires knowledge of the swift python code and may not succeed.</para>
        </warning>
        <para>First, load the ring and a new ringbuilder object in a Python REPL:</para>
        <programlisting language="python">>>> from swift.common.ring import RingData, RingBuilder
>>> ring = RingData.load('/path/to/account.ring.gz')</programlisting>
        <para>Now, start copying the data we have in the ring into the builder.</para>
        <programlisting language="python">
>>> import math
>>> partitions = len(ring._replica2part2dev_id[0])
>>> replicas = len(ring._replica2part2dev_id)

>>> builder = RingBuilder(int(Math.log(partitions, 2)), replicas, 1)
>>> builder.devs = ring.devs
>>> builder._replica2part2dev = ring.replica2part2dev_id
>>> builder._last_part_moves_epoch = 0
>>> builder._last_part_moves = array('B', (0 for _ in xrange(self.parts)))
>>> builder._set_parts_wanted()
>>> for d in builder._iter_devs():
            d['parts'] = 0
>>> for p2d in builder._replica2part2dev:
            for dev_id in p2d:
                builder.devs[dev_id]['parts'] += 1</programlisting>
        <para>This is the extent of the recoverable fields. For
            <literal>min_part_hours</literal>  you'll either have to remember what the
            value you used was, or just make up a new one.</para>
        <programlisting language="python">
>>> builder.change_min_part_hours(24) # or whatever you want it to be</programlisting>
        <para>Try some validation: if this doesn't raise an exception, you may feel some
            hope. Not too much, though.</para>
        <programlisting language="python">>>> builder.validate()</programlisting>
        <para>Save the builder.</para>
        <programlisting language="python">
>>> import pickle
>>> pickle.dump(builder.to_dict(), open('account.builder', 'wb'), protocol=2)</programlisting>
        <para>You should now have a file called 'account.builder' in the current working
            directory. Next, run <literal>swift-ring-builder account.builder write_ring</literal>
            and compare the new account.ring.gz to the account.ring.gz that you started
            from. They probably won't be byte-for-byte identical, but if you load them up
            in a REPL and their <literal>_replica2part2dev_id</literal> and
            <literal>devs</literal> attributes are the same (or nearly so), then you're
            in good shape.</para>
        <para>Next, repeat the procedure for <filename>container.ring.gz</filename>
            and <filename>object.ring.gz</filename>, and you might get usable builder files.</para>
    </section>
</section>