[Linux-cluster] Re: If I have 5 GNBD server?

[Fajar A. Nugraha]

brianu wrote:

> Hello all,
>
>  
>
> This is a question I have basically been asking, the question on why 
> you would want to do it is failover, the docs at 
> http://sourceware.org/cluster/gnbd/gnbd_usage.txt state that 
> dm-multipath is an option for gnbd,
>
I'm not sure about dm-multipath. The thing is, when a gnbd server dies, 
instead of saying "read/write failed" as normal block device does, gnbd 
simply retries the request and tries to reconnect if it's disconnected. 
Forever.

> and documents elsewhere also indicate that GNBD can be configured as a 
> redundancy, yet I cannot find any documentation on how to configure it.
>
>  
>
> If using LVM to make a volume of imported gnbds is not the answer for 
> redundancy can anyone suggest a method that is? Im not opposed to 
> using any other resource of cluster or GFS but I would really like to 
> implement a redundant solution, ( gnbd, gulm, etc.).
>
>  
>
It would be possible if you have at least two servers, connected to the 
same storage, running as gnbd server and exporting the same block devices.

You need to have one IP address that can failover to any available node 
(use rgmanager or keepalived to achieve this). That way, if one server 
node dies the IP address will be moved to the other node. Client will be 
disconnected, but since gnbd-import will automatically reconnect (it 
actually connects to a different node since the gnbd server IP address 
was moved) the process will be transparent to the client (all they see 
is a slight delay during reconnect).

Regards,

Fajar