[Linux-cluster] Cluster with shared storage on low budget

[Gordan Bobic]

Nikola Savic wrote:
> Gordan Bobic wrote:
>> Something else just occurs to me - you mentioned MySQL. You do realize
>> that the performance of it will be attrocious on a shared cluster file
>> system (ANY shared cluster file system), right? Unless you only intend
>> to run mysqld on a single node at a time (in which case there's no
>> point in putting it on a cluster file system). 
> 
>   MySQL Master and Slave(s) will run on single node. No two MySQL
> instances will run on same set of data. Shared storage for MySQL data
> should enable easier movement of MySQL instance between nodes. Eg. when
> MySQL master needs to be moved from one node to other, I assume it would
> be easier with DRBD, because I would "only" need to stop MySQL on one
> node and start it on other configured to use same set of data.

There is a better way to do that. Run DRBD in active-passive mode, and 
grab the fail-over scripts from heartbeat. Then set up a dependency in 
cluster.conf that will handle a combined service of DRBD disk (handling 
active/passive switch), file system (mounting the fs once the DRBD 
becomes active locally, and mysql. You define them as dependant on each 
other in cluster.conf by suitable nesting.

> Additionally, floating IP address assigned to MySQL master would need to
> be re-assigned to new node.

You can make that IP a part of the dependency stack mentioned above.

> Slaves would also need to be restarted to
> connect to new master. Even without floating IP used only my MySQL
> Master, slaves and web application can easily be reconfigured to use new
> IP. Do you see problem in this kind of setup?

If the IP fails over and the FS is consistent you don't need to change 
any configs - MySQL slaves will re-try connecting until they succeed. 
Just make sure your bin-logs are on the same mount as the rest of MySQL, 
since they have to fail over with the rest of the DB.

Gordan