[CentOS] file system replication

[Jason T. Slack-Moehrle]

Hi John,

On Thu, Oct 9, 2014 at 12:53 PM, John R Pierce <pierce at hogranch.com> wrote:

> 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.


​Thank you for this info. This clears up a lot and is very helpful.

Jason