[CentOS] file system replication

Thu Oct 9 19:53:44 UTC 2014
John R Pierce <pierce at hogranch.com>

On 10/9/2014 11:57 AM, Jason T. Slack-Moehrle wrote:
> ​Just to clarify. What state is the slave in?
>
> If master goes down, how does the slave become active? Just reboot it and
> let it come up? The wording "slave copy can't be mounted until drdb is
> stopped" leads me to believe the slave is in some alternate state to be
> receiving the blocks of data.

the slave is up and running, but the file systems you're replicating are 
unmounted, and its services are stopped, so you could consider this to 
be a 'standby' state.

yes, to use drbd, its important that you put your email spools, 
databases, etc, on dedicated file system(s), NOT on the OS root file 
system.   I generally use lvm for all this.

a cluster management package, such as the ones suggested by another 
poster, would take care of all this for you (once you have things setup 
properly), if the master fails, it would 'activate' the slave, switch 
its IP[*] over to be the 'production' system, and mount its file 
systems, starting its services (mysqld, postfix, etc) per your 
configuration.

[*] typically, you use THREE IP addresses for a HA cluster.   a unique 
IP for each system, used only for management, and a 'service' IP used 
for the production accesses, which is held by the currently active 
system.   when the master fails, the slave adopts this service IP.


-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast