Crucial Paradigm Australia Official Blog
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If you ever find your server won’t exist maintenance mode after a power failure, or even just normally you may have a corrupt state.db file.
The error message you may get while trying to make a change on the node is:
Cannot forward messages because the host cannot be contacted. The host may be switched off or there may be network connectivity problems.
If this is in fact a state.db corruption in a pool, you can try the following steps to fix the issue:
- cd /var/xapi
- ls -al -> check the results of this, usually the state.db will have an old time stamp – the time at which is became corrupted.
- mv state.db state.db_bak
- service xapi restart
If this does not fix the issue, I’ve heard of users opening state.db with an xml editor (its just an xml file) and fixing the errors in the xml file. Some other users have mentioned that the cause of the issue could be that the config in the node that is down in maintenance mode could have the incorrect config in /etc/xensource/pool.conf. The format should be “slave:[masterip]“.
Found an interesting article here regarding Youtube’s hosting architecture. Quite simple actually: http://highscalability.com/youtube-architecture
Youtube has over 1billion views per day, so quite impressive setup!