External storage/Maintenance
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![]() | This page was last updated in 2008 and may be outdated. Please update it if you can. |
How to safety perform maintenance on external storage boxes...
ES boxes are Apaches running an instance of MySQL for some simple blob storage. A couple of things you need to know:
- They come in clusters.
- You can check /h/w/php-1.5/db.php for cluster<->machine assignments
- Each cluster has a master and one or more slaves.
- The master is the first to appear in the cluster's list in db.php... but for some perverse reason is usually the highest-numbered server (eg, srv146 master, 145 and 144 slaves)
- It should always be safe to take down a slave for maintenance.
- For older, read-only clusters, taking the master down is also safe. Reads will fail-over to the slaves.
- Only the last couple clusters are active for writes.
- These are listed in $wgDefaultExternalStore at the end of db.php
- If you're going to shut down the master of one of these clusters, you should remove it from $wgDefaultExternalStore temporarily, otherwise some page saves will fail while it's down.
- If MySQL doesn't automatically start when you reboot the machine, punch it manually!
- /etc/init.d/mysqld start should usually do it.
In rarer cases it may be necessary to fix replication or re-clone databases to replace a dead slave. These exercises are left to the reader.