[Linux-cluster] GFS is for what and how it works ?

[Halomoan]

Sorry, I'm newbie in GFS.

Followed Redhat's GFS documentation 
To find out how GFS works, I have 2 nodes (node A and node B) for GFS and 1 node (node C) for GNBD server. It runs with no error but i don't know how to use it (GFS)

I attached my /etc/cluster/cluster.conf below.

My question is:

1. At a time, how many nodes have GFS filesystem mounted ? Where is the cluster's work in GFS ?
2. How do I shared the GFS filesystem to other server ? Do I need other software ?
3. From this configuration, if node A failed, what happen to the GFS filesystem ? failover to node B ? How about with the other server that is using the GFS filesystem in node A ?
4. Could you give me example what is actually the GFS real usage in real live ? 

I'm absolutely confuse with this GFS on how they works.

Thanks

Regards,

Halomoan

--------------------- Cluster.conf ------------------------
<?xml version="1.0"?>
<cluster config_version="14" name="gfs_cluster">
        <fence_daemon post_fail_delay="0" post_join_delay="3"/>
        <clusternodes>
                <clusternode name="p3" votes="1">
                        <fence>
                                <method name="1">
                                        <device name="byhand" nodename="p3"/>
                                </method>
                        </fence>
                </clusternode>
                <clusternode name="p7" votes="1">
                        <fence>
                                <method name="1">
                                        <device name="byhand" nodename="p7"/>
                                </method>
                        </fence>
                </clusternode>
        </clusternodes>
        <cman expected_votes="1" two_node="1"/>
        <fencedevices>
                <fencedevice agent="fence_gnbd" name="p5_gnbd" servers="p5.xxx.com"/>
                <fencedevice agent="fence_manual" name="byhand"/>
        </fencedevices>
        <rm>
                <failoverdomains>
                        <failoverdomain name="failover" ordered="0" restricted="0">
                                <failoverdomainnode name="p3" priority="1"/>
                                <failoverdomainnode name="p7" priority="1"/>
                        </failoverdomain>
                </failoverdomains>
                <resources>
                        <clusterfs device="/dev/gnbd/global_disk" force_unmount="1" fsid="15674" fstype="gfs" mountpoint="/data" name="data" options=""/>
                </resources>
                <service autostart="1" domain="failover" name="test">
                        <clusterfs ref="data"/>
                </service>
        </rm>
</cluster>

 

 
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